Semiconductor device

ABSTRACT

A semiconductor device includes a lead frame, a transistor, and an encapsulation resin. The lead frame includes a drain frame, a source frame, and a gate frame. The drain frame includes drain frame fingers. The source frame includes source frame fingers. The drain frame fingers and the source frame fingers are alternately arranged in a first direction and include overlapping portions as viewed from a first direction. In a region where each drain frame finger overlaps the source frame fingers as viewed in the first direction, at least either one of the drain frame fingers and the source frame fingers are not exposed from the back surface of the encapsulation resin.

BACKGROUND ART

The present invention relates to a semiconductor device.

A semiconductor device includes a transistor, a die pad on whichtransistor is arranged, a lead frame, a bonding wire that connects eachelectrode of a transistor to a lead frame, and an encapsulation resinthat encapsulates the transistor and the bonding wire (refer to, forexample, Japanese Laid-Open Patent Publication No. 2012-178416).

The bonding wire connecting each electrode of the transistor to the leadframe may increase the inductance.

SUMMARY OF THE INVENTION

It is an object of the present invention to limit increases in theinductance.

To achieve the above object, a semiconductor device includes a leadframe, a transistor, and an encapsulation resin. The transistor includesa plurality of drain electrode pads, a plurality of source electrodepads, and a gate electrode pad on one surface. Each of the electrodepads faces a front surface of the lead frame and is connected to thelead frame. The encapsulation resin is rectangular and encapsulates thetransistor and the lead frame so that part of the lead frame is exposedfrom a back surface. The lead frame includes a drain frame electricallyconnected to the drain electrode pads, a source frame electricallyconnected to the source electrode pads, and a gate frame electricallyconnected to the gate electrode pads. The drain frame includes aplurality of drain frame fingers. The drain frame fingers are spacedapart from each other in a first direction, extended in a seconddirection that is orthogonal to the first direction in a plan view, andconnected to the drain electrode pad. The source frame includes aplurality of source frame fingers. The source frame fingers are spacedapart from each other in the first direction, extended in the seconddirection, and connected to the source electrode pad. The drain framefingers and the source frame fingers are alternately arranged in thefirst direction and include a portion that overlaps each other as viewedin the first direction. In a region where the drain frame fingers andthe source frame fingers overlap one another as viewed in the firstdirection, at least either one of the drain frame fingers and the sourceframe fingers are not exposed from the back surface of the encapsulationresin.

BRIEF DESCRIPTION OF DRAWINGS

The invention, together with objects and advantages thereof, may best beunderstood by reference to the following description of the presentlypreferred embodiments together with the accompanying drawings in which:

FIG. 1 is a perspective view of a first embodiment of a semiconductordevice.

FIG. 2 is a plan view of a transistor in the semiconductor device ofFIG. 1;

FIG. 3 is a plan view of a lead frame in the semiconductor device ofFIG. 1;

FIG. 4 is a perspective view of the lead frame of FIG. 3;

FIG. 5 is a cross-sectional view taken along line 5-5 in FIG. 3

FIG. 6 is a cross-sectional view taken along line 6-6 in FIG. 3;

FIG. 7 is a side view of FIG. 3;

FIG. 8 is a plan view of a state in which the transistor is mounted onthe lead frame;

FIG. 9 is a bottom view of the semiconductor device of FIG. 1;

FIG. 10 is a flowchart showing a method for manufacturing thesemiconductor device;

FIG. 11 is a bottom view of an existing semiconductor device;

FIG. 12 is a perspective view showing a state in which the semiconductordevice is mounted on land patterns of a circuit substrate;

FIG. 13 is a plan view of one portion of the transistor;

FIG. 14A is a partially enlarged plan view of FIG. 13;

FIG. 14B is a partially enlarged plan view of FIG. 13;

FIG. 15 is a cross-sectional view taken along line 15-15 in FIG. 14A;

FIG. 16 is a circuit diagram of a DC/DC converter using thesemiconductor device;

FIG. 17 is a plan view of a lead frame for a second embodiment of thesemiconductor device;

FIG. 18 is a plan view of a transistor mounted on the lead frame of FIG.17;

FIG. 19 is a perspective view of a third embodiment of the semiconductordevice;

FIG. 20 is an exploded perspective view of the semiconductor device ofFIG. 19;

FIG. 21 is a cross-sectional view taken along line 21-21 in FIG. 19;

FIG. 22 is a plan view of a lead frame for a fourth embodiment of thesemiconductor device;

FIG. 23 is a bottom view of the semiconductor device including the leadframe of FIG. 22;

FIG. 24 is a plan view of a lead frame for a modified example of thesemiconductor device;

FIG. 25 is a bottom view of the semiconductor device including the leadframe of FIG. 24;

FIG. 26 is a plan view of a lead frame for a modified example of thesemiconductor device;

FIG. 27 is a bottom view of the semiconductor device including the leadframe of FIG. 26;

FIG. 28 is a plan view of a lead frame for a modified example of thesemiconductor device;

FIG. 29 is a bottom view of the semiconductor device including the leadframe of FIG. 28;

FIG. 30 is a plan view of one portion of a lead frame for a modifiedexample of the semiconductor device;

FIG. 31 is a plan view of a lead frame for a modified example of thesemiconductor device;

FIG. 32 is a plan view of a transistor for a modified example of thesemiconductor device; and

FIG. 33 is a schematic plan view showing a relationship of a drainelectrode, a source electrode, and a gate electrode of a transistor fora modified example of the semiconductor device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of a semiconductor device will be hereinafter describedwith reference to the drawings. The embodiment described belowillustrates a configuration and a method for embodying a technical idea,and is not provided to limit the material, shape, structure,arrangement, dimension, and the like of each configuring component tothe following. Various modifications can be made with the embodimentsdescribed hereafter within the scope of the claims.

First Embodiment

Semiconductor Device

As shown in FIG. 1, a semiconductor device 1 includes a lead frame 10for electrically connecting to a circuit substrate 300 (not illustratedin FIG. 1, see FIG. 11), a transistor 20 mounted on the lead frame 10,and an encapsulation resin 30 that encapsulates the transistor 20. Thetransistor 20 is a High Electron Mobility Transistor (HEMT) that uses anitride semiconductor. The semiconductor device 1 includes a package(encapsulation resin 30) in which a dimension in a first direction X,which becomes a lateral direction of the semiconductor device 1, isabout 5 mm, a dimension in a second direction Y, which becomes alongitudinal direction of the semiconductor device 1, is about 6 mm, anda height direction Z of the semiconductor device 1 is about 0.6 mm. Thesemiconductor device 1 is a surface mounting type, and is a so-calledSmall Outline Package (SOP) in which the lead frame is taken out fromtwo directions of the encapsulation resin 30.

The usage frequency range of the semiconductor device 1 is greater thanor equal to 1 MHz and less than or equal to 100 MHz, and is preferablygreater than or equal to 1 MHz and less than or equal to 30 MHz. Thesemiconductor device 1 of the present embodiment is used at 30 MHz.Furthermore, the semiconductor device 1 can be applied to a circuit inwhich a range of a drain current is a range of greater than or equal to1 A and less than or equal to 200 A, and is preferably applied to acircuit in which a range of the drain current is a range of greater thanor equal to 10 A and less than or equal to 100 A.

The encapsulation resin 30, for example, is made of an epoxy resin andhas the form of a quadrangular plate. The encapsulation resin 30includes a front surface 31 that becomes a top surface, and a backsurface 32 that becomes a bottom surface opposing the front surface 31in the height direction Z. The back surface 32 becomes a surface mountedon the circuit substrate 300. The encapsulation resin 30 also includes afirst lateral side surface 33 that becomes a side surface on one side inthe first direction X, a second lateral side surface 34 that becomes aside surface on the other side in the first direction X, a firstlongitudinal side surface 35 that becomes a side surface on one side inthe second direction Y, and a second longitudinal side surface 36 thatbecomes a side surface on the other side in the second direction Y.

The transistor 20 has the form of a quadrangular plate. The transistor20 has a rectangle shape in a plan view. The transistor 20 is mounted onthe lead frame 10 so that the first direction X becomes the longitudinaldirection. As shown in FIG. 2, one example of an outer shape size of thetransistor 20 is a rectangle having a longitudinal to lateral ratio of2:1 in which a length L1 of one side in the longitudinal direction isabout 4200 μm, and a length L2 of another side is about 2100 μm in aplan view. In the following description of the transistor 20, the frameof reference for directions will be a state in which the transistor 20is mounted on the lead frame 10.

The transistor 20 includes a front surface 20 a, which is the surfacelocated at the side of the lead frame 10 (see FIG. 1), and a backsurface 20 b (see FIG. 1), which is the other surface opposing the frontsurface 20 a. Five drain electrode pads 21, four source electrode pads22, and one gate electrode pad 23 electrically connected with the leadframe 10 are arranged on the front surface 20 a. The drain electrodepads 21 include four drain electrode pads 21P in which a length LD inthe longitudinal direction is long, and one drain electrode pad 21Q inwhich a length LDE in the longitudinal direction is short. There may beany number of the drain electrode pads 21, source electrode pads 22, andgate electrode pads 23. Thus, for example, the number of drain electrodepads 21 may differ from the number of source electrode pads 22. Thetransistor 20 may include a plurality of gate electrode pads 23. In thefollowing description, when referring to all of the five drain electrodepads, they will be referred to as the drain electrode pads 21.

As shown in FIG. 2, the drain electrode pads 21 and the source electrodepads 22 are alternately arranged in the longitudinal direction (firstdirection X) of the transistor 20 in a plan view. The drain electrodepads 21 and the source electrode pads 22 are each formed to besubstantially rectangular elongated in a longitudinal direction that isthe direction (second direction Y) orthogonal to the longitudinaldirection of the transistor 20. The drain electrode pads 21 and thesource electrode pads 22 are parallel to one another. A drain electrodepad 21 is arranged at each of the two ends of the transistor 20 in thefirst direction X.

The gate electrode 23 is arranged at one end of the transistor 20 in thefirst direction X. The gate electrode 23 faces the drain electrode pad21Q arranged at one end of the transistor 20 in the first direction Xspaced apart by a gap in the second direction Y. The gate electrode pad23 is arranged closer to one end of the transistor 20 in the seconddirection Y, and the drain electrode pad 21Q is arranged closer to theother end of the transistor 20 in the second direction Y.

The length LD of the four drain electrode pads 21P and the length LS ofthe four source electrode pads 22 are equal to each other. The lengthLDE of the drain electrode pad 21Q is less than or equal to one-half ofthe length LD. The length LG of the gate electrode pad 23 is equal tothe length LDE. A width WD of the drain electrode pads 21, a width WS ofthe source electrode pads 22, and a width WG of the gate electrode pad23 are equal to one another. The drain electrode pads 21, the sourceelectrode pads 22, and the gate electrode pads 23 each have two ends inthe second direction Y that are arcuate and bulged outward in the seconddirection Y.

The drain electrode pads 21 are arranged at equal intervals in the firstdirection X, and the source electrode pads 22 are arranged at equalintervals in the first direction X. The four drain electrode pads 21Pand the four source electrode pads 22 are arranged at correspondingpositions in the second direction Y. The distance Dds from each drainelectrode pad 21 to the adjacent source electrode pad 22 in the firstdirection X is the same. The distance Dsg from the gate electrode pad 23to the adjacent source electrode pad 22 in the first direction X isequal to the distance Dds.

The dimensions of the transistor 20 of FIG. 2 are as follows.

The length LD of each of the four drain electrode pads 21P and thelength LS of each the four source electrode pads 22 are about 1760 μm,and the length LDE of the drain electrode pad 21Q is about 755 μm. Thelength LG of the gate electrode pad 23 is about 755 μm. The width WD ofeach of the drain electrode pads 21, the width WS of each of the sourceelectrode pads 22, and the width WG of the gate electrode pad 23 isabout 240 μm.

The distance Ddg between the gate electrode pad 23 and the drainelectrode pad 21Q in the second direction Y is about 250 μm. Thedistance Dds between each drain electrode pad 21 and the adjacent sourceelectrode pad 22 in the first direction X is about 200 μm. The distanceDsg between the gate electrode pad 23 and the adjacent source electrodepad 22 in the first direction X is about 200 μm.

As shown in FIG. 3, the lead frame 10 includes a drain frame 11electrically connected to the drain electrode pads 21 (see FIG. 2), asource frame 12 electrically connected to the source electrode pad 22(see FIG. 2), and a gate frame 13 electrically connected to the gateelectrode pad 23 (see FIG. 2). The drain frame 11, the source frame 12,and the gate frame 13 are each formed by, for example, etching a copperplate. The drain frame 11, the source frame 12, and the gate frame 13are electrically insulated from each other by gaps extending in between.

The drain frame 11 is arranged closer to the first longitudinal sidesurface 35 of the encapsulation resin 30 (shown by double-dashed line ofFIG. 3) in a plan view. The drain frame 11 includes four drain terminals11 a, a drain coupling portion 11 b that couples the drain terminals 11a, and five drain frame fingers 11 c extending from the drain couplingportion 11 b toward the second longitudinal side surface 36 in thesecond direction Y. The drain frame fingers 11 c extended in the seconddirection Y. Thus, the drain frame 11 is comb-shaped. The four drainterminals 11 a, the drain coupling portion 11 b, and the five drainframe fingers 11 c are, for example, formed from the same member. Theremay be any number of the drain terminals 11 a and any number of thedrain frame fingers 11 c. For example, the number of drain terminals 11a may be the same as or differ from the number of drain frame fingers 11c. Furthermore, the number of drain frame fingers 11 c is preferably setaccording to the number of drain electrode pads 21 of the transistor 20of FIG. 2.

The drain terminals 11 a are each rectangular and elongated in alongitudinal direction that is the second direction Y in a plan view.The drain terminals 11 a are arranged at equal intervals in the firstdirection X. The drain terminals 11 a are arranged at positions adjacentto the first longitudinal side surface 35 of the encapsulation resin 30.One end of each drain terminal 11 a projects out of the encapsulationresin 30 from the first longitudinal side surface 35 in the seconddirection Y. The other end of the drain terminal 11 a is coupled to thedrain coupling portion 11 b in the second direction Y.

The drain coupling portion 11 b couples the four drain terminals 11 aand the five drain frame fingers 11 c. The drain coupling portion 11 bextends in the first direction X. The width WCD of the drain couplingportion 11 b (dimension of the drain coupling portion 11 b in the seconddirection Y) is smaller than the width WTD of the drain terminal 11 a(dimension of the drain terminal 11 a in the first direction X). Firsttie bar portion 11 d that couple a steel plate (not illustrated) and thedrain frame 11 when forming the drain frame 11 from the steel plate,which serves as a base material, are integrated with the drain couplingportion 11 b at the two ends of the drain coupling portion 11 b in thefirst direction X. The first tie bar portions 11 d extended in the firstdirection X from both ends of the drain coupling portion 11 b. One firsttie bar portion 11 d extends from the drain coupling portion 11 b to thefirst lateral side surface 33. The other first tie bar portion 11 dextends from the drain coupling portion 11 b to the second lateral sidesurface 34.

The drain frame fingers 11 c and the drain terminals 11 a are arrangedat opposite sides of the drain coupling portion 11 b. The drain framefingers 11 c include four drain frame fingers 11P in which the lengthLFD in the second direction Y is long, and one drain frame finger 11Q inwhich the length LFDE in the second direction Y is short. In thefollowing description, when referring to all of the five drain framefingers, they will be referred to as the drain frame fingers 11 c.

The drain frame fingers 11 c are arranged at equal intervals in thefirst direction X. The distance between adjacent drain frame fingers 11c in the first direction X is shorter than the distance between theadjacent drain terminals 11 a in the first direction X. In the firstdirection X, the center of each of the drain frame fingers 11 c at thetwo ends is located inward from the center of each of the drainterminals 11 a at the two ends. As viewed in the second direction Y, thedrain frame fingers 11 c located at the two ends in the first directionX are partially overlapped with the drain terminals 11 a located at thetwo ends in the first direction X. The middle one of the drain framefingers 11 c in the first direction X is located at the middle of theencapsulation resin 30 in the first direction X.

Each drain frame finger 11 c includes two regions having differentwidths. The drain frame finger 11 c includes a first section 11 m and asecond section 11 n. The first section 11 m has a larger width and islocated closer to the drain coupling portion 11 b. Further, the firstsection 11 m extends from the drain coupling portion 11 b to a positionlocated slightly closer to the drain coupling portion 11 b from themiddle of the encapsulation resin 30 in the second direction Y. Thesecond section 11 n has a smaller width. The second section 11 n and thedrain coupling portion 11 b are located at opposite sides of the firstsection 11 m. The width WFD1 of the first section 11 m is equal in eachdrain frame finger 11 c. A width WFD2 of the second section 11 n of eachdrain frame finger 11 c is equal to each other. The width WFD1 of thefirst section 11 m is greater than the width WCD of the drain couplingportion 11 b. The width WFD2 of the second section 11 n is smaller thanthe width WCD of the drain coupling portion 11 b. The length of thefirst section 11 m in the second direction Y is equal in each drainframe finger 11 c. The first section 11 m may have any width WFD1, andthe drain coupling portion 11 b may have any width WCD. For example, thewidth WFD1 of the first section 11 m may be equal to the width WCD ofthe drain coupling portion 11 b. Furthermore, the width WCD of the draincoupling portion 11 b may be equal to the width WFD2 of the secondsection 11 n.

As shown in FIG. 3, a distal portion 11 h of each drain frame finger 11Pis proximate to a source coupling portion 12 b, which will be describedlater, of the source frame 12 in the second direction Y. Each drainframe finger 11P faces the source coupling portion 12 b in the seconddirection Y.

The drain frame finger 11P located closest to the first lateral sidesurface 33 and the drain frame finger 11Q include second tie barportions 11 i and 11 j, respectively. The second tie bar portion 11 iprovided on the drain frame finger 11P extends in the second direction Yfrom the middle of the encapsulation resin 30 in the second direction Ytoward the first lateral side surface 33. The second tie bar portion 11i is exposed from the first lateral side surface 33. The second tie barportion 11 j of the drain frame finger 11Q extends in the seconddirection Y from the middle of the encapsulation resin 30 in the seconddirection Y toward the second lateral side surface 34. The second tiebar portion 11 j is exposed from the second lateral side surface 34.

The source frame 12 is arranged closer to the second longitudinal sidesurface 36 of the encapsulation resin 30 in a plan view. The sourceframe 12 is also arranged closer to the first lateral side surface 33 ofthe encapsulation resin 30 in a plan view. The source frame 12 includesthree source terminals 12 a, the source coupling portion 12 b thatcouples the source terminals 12 a, and four source frame fingers 12 cextending from the source coupling portion 12 b toward the firstlongitudinal side surface 35 in the second direction Y. The source framefingers 12 c extend in the second direction Y. Thus, the source frame 12is comb-shaped. The plurality of source terminals 12 a, the sourcecoupling portion 12 b, and the plurality of source frame fingers 12 care, for example, formed from the same member. There may be any numberof source terminals 12 a and any number of source frame fingers 12 c.For example, the number of source terminals 12 a may be the same as ordiffer from the number of source frame fingers 12 c. Furthermore, thenumber of source frame fingers 12 c is preferably set according to thenumber of source electrode pads 22 of the transistor 20 of FIG. 2.

The source terminal 12 a is rectangular and elongated in a longitudinaldirection that is the second direction Y in a plan view. The sourceterminals 12 a are arranged at equal intervals in the first direction X.The source terminals 12 a are arranged at positions adjacent to thesecond longitudinal side surface 36 of the encapsulation resin 30. Oneend of each source terminal 12 a projects out of the encapsulation resin30 from the second longitudinal side surface 36 in the second directionY. The other end of the source terminal 12 a is coupled to the sourcecoupling portion 12 b in the second direction Y. The positions of thesource terminals 12 a in the first direction X corresponds to thepositions of the drain terminal 11 a in the first direction X. The widthWTS of the source terminals 12 a (dimension of the source terminals 12 ain the first direction X) is equal to the width WTD of the drainterminals 11 a.

The source coupling portion 12 b couples the three source terminals 12 aand the four source frame fingers 12 c. The source coupling portion 12 bextends in the first direction X. The width WCS of the source couplingportion 12 b (dimension of the source coupling portion 12 b in thesecond direction Y) is smaller than the width WTS of the sourceterminals 12 a and the width WCD of the drain coupling portion 11 b.Further, the width WCS is equal to the width WFD2 of the second section11 n of each drain frame finger 11 c. A tie bar portion 12 d thatcouples a steel plate (not illustrated) and the source frame 12 whenforming the source frame 12 from a steel plate (not illustrated), whichserves as a base material, is arranged on the source coupling portion 12b at the end closer to the first lateral side surface 33. The tie barportion 12 d extends in the first direction X from the end of the sourcecoupling portion 12 b to the first lateral side surface 33.

The source frame fingers 12 c and the source terminals 12 a are arrangedat opposite sides of the source coupling portion 12 b. The source framefingers 12 c are arranged at equal intervals in the first direction X.The distance between adjacent frame fingers 12 c in the first directionX is shorter than the distance between adjacent source terminals 12 a inthe first direction X. The distance between the adjacent source framefingers 12 c in the first direction X is also equal to the distancebetween the adjacent drain frame fingers 11 c in the first direction X.The length LFS of the source frame finger 12 c is shorter than thelength LFD of the drain frame fingers 11P and the length LFDE of thedrain frame finger 11Q. Each source frame finger 12 c is arrangedbetween the drain frame fingers 11 c that are adjacent to each other inthe first direction X. A distal end of the source frame finger 12 c islocated closer to the second longitudinal side surface 36 of theencapsulation resin 30 than the first section 11 m of each drain framefinger 11 c. In other words, as viewed in the first direction X, eachsource frame finger 12 c is overlapped with the second section 11 n ofeach drain frame finger 11 c but not with the first section 11 m. Thesource frame fingers 12 c are parallel to the drain frame fingers 11 c.The distance DFds between each source frame finger 12 c and the adjacentdrain frame finger 11 c is equal. The width WFS of the source framefingers 12 c is equal. The width WFS is equal to the width WCS of thesource coupling portion 12 b. The width WFS is also equal to the widthWFD2 of the second section 11 n of each drain frame finger 11 c.

The gate frame 13 is arranged closer to the second longitudinal sidesurface 36 of the encapsulation resin 30 in a plan view. The gate frame13 is also arranged closer to the second lateral side surface 34 of theencapsulation resin 30 in a plan view. The gate frame 13 includes a gateterminal 13 a, a gate coupling portion 13 b, and a gate frame finger 13c. The gate frame 13 is adjacent to the source frame 12 in the firstdirection X.

The gate terminal 13 a is rectangular and elongated in shape in alongitudinal direction that is the second direction Y in a plan view.The gate terminal 13 a is arranged at a position adjacent to the secondlongitudinal side surface 36 of the encapsulation resin 30. One end ofthe gate terminal 13 a projects out of the encapsulation resin 30 fromthe second longitudinal side surface 36 in the second direction Y. Theother end of the gate terminal 13 a is coupled to the gate couplingportion 13 b in the second direction Y. The position of the gateterminal 13 a in the first direction X corresponds to the position ofthe drain terminal 11 a located closest to the second lateral sidesurface 34. The width WTG of the gate terminal 13 a (dimension of thegate terminal 13 a in the first direction X) is equal to the width WTDof the drain terminals 11 a.

The gate coupling portion 13 b couples the gate terminal 13 a and thegate frame finger 13 c. The position of the gate coupling portion 13 bin the second direction Y corresponds to the position of the sourcecoupling portion 12 b in the second direction Y. The width WCG of thegate coupling portion 13 b (dimension of the gate coupling portion 13 bin the second direction Y) is smaller than the width WTG of the gateterminal 13 a. The width WCG of the gate coupling portion 13 b is equalto the width WCS of the source coupling portion 12 b. A tie bar portion13 d that couples a steel plate (not illustrated) and the gate frame 13when forming the gate frame 13 from a steel plate, which serves as abase material, is arranged on the gate coupling portion 13 b at the endcloser to the second lateral side surface 34. The tie bar portion 13 dextends in the first direction X from the end of the gate couplingportion 13 b to the second lateral side surface 34.

The gate frame finger 13 c and the gate coupling portion 13 b arelocated at opposite sides of the gate terminal 13 a. The gate framefinger 13 c extends in the second direction Y from the end of the gatecoupling portion 13 b located closer to the first lateral side surface33. The length LFG of the gate frame finger 13 c is shorter than thelength LFS of the source frame finger 12 c.

The position of the gate frame finger 13 c in the first direction Xcorresponds to the position of the drain frame finger 11Q in the firstdirection X. The gate frame finger 13 c is parallel to the source framefingers 12 c. The gate frame finger 13 c is arranged closer to thesecond longitudinal side surface 36 than the drain frame finger 11Q. Inother words, in the second direction Y, a distal end of the gate framefinger 13 c faces the distal end of the drain frame finger 11Q. Thus,the distance DFgs between the gate frame finger 13 c and the adjacentsource frame finger 12 c in the first direction X is equal to thedistance DFds. The width WFG of the gate frame finger 13 c is equal tothe width WCG of the gate coupling portion 13 b. The width WFG is alsoequal to the width WFD2 of the second section 11 n of the drain framefinger 11 c.

As can be understood from FIG. 4, the drain frame 11, the source frame12, and the gate frame 13 each include a thin portion. The shading inFIG. 3 indicates the thin portion in each of the drain frame 11, thesource frame 12, and the gate frame 13. The thin portion in each of thedrain frame 11, the source frame 12, and the gate frame 13 is formedthrough, for example, a half-etching process.

As shown in FIG. 5, the thickness TD1 of the distal portion 11 h of eachdrain frame finger 11P in the drain frame 11 is less than the thicknessTD2 of portions other than the distal portion 11 h in the second section11 n of each drain frame finger 11P. In the present embodiment, thethickness TD1 is one-half the thickness TD2. The thickness TD2 is themaximum thickness of the drain frame finger 11 c. The first section 11 mof each drain frame 11 includes a thick base 11 r and thin flanges 11 sarranged on opposite sides of the base 11 r in the first direction X.The width of the base 11 r is equal to the width WFD2 of the secondsection 11 n. The thickness TD4 of the base 11 r is equal to thethickness TD2, and the thickness TD5 of the flanges 11 s is equal to thethickness TD1. The thickness of each drain terminal 11 a is equal to thethickness TD2.

The thickness TD5 of an end 11 k of the drain coupling portion 11 b atthe side closer to the second longitudinal side surface 36 of theencapsulation resin 30 and the thickness TD3 (see FIG. 4) of each of thetie bar portions 11 d, 11 i, and 11 j in the drain frame 11 are lessthan the thickness TD2 and equal to the thickness TD1. Thus, in thedrain frame 11, the thicknesses TD1 and TD3 of the distal portion 11 hof each drain frame finger 11P and each of the tie bar portions 11 d, 11i, and 11 j are less than the thickness TD2 of the other portions of thedrain frame 11. As shown in FIG. 3, in the present embodiment, thedistal portion 11 h of each drain frame finger 11P projects furthertoward the second longitudinal side surface 36 from the drain framefinger 11Q in the second direction Y.

As shown in FIG. 6, in the source frame 12, each source frame finger 12c entirely has a thickness TS1 that is is less than the thickness TS2 ofthe source terminals 12 a. In the present embodiment, the thickness TS1is one-half of the thickness TS2. The thickness of the source couplingportion 12 b is less than the thickness TS2 and equal to the thicknessTS1 of each source frame finger 12 c. The thickness TS3 (see FIG. 4) ofthe tie bar portion 12 d is equal to the thickness TS1. Thus, in thesource frame 12, the thickness TS1 of each source frame finger 12 c andthe source coupling portion 12 b and the thickness TS3 of the tie barportion 12 d are less than the thickness TS2 of the source terminal 12a. The thickness TS1 of each source frame finger 12 c and the sourcecoupling portion 12 b and the thickness TS3 of the tie bar portion 12 dare equal to the thicknesses TD1 and TD3 (see FIG. 5) of the drain frame11. The thickness TS2 of the source terminal 12 a is equal to thethickness TD2 (see FIG. 5) of the drain frame 11.

As shown in FIG. 7, in the gate frame 13, the entire gate frame finger13 c has a thickness TG1 that is less than the thickness TG2 of the gateterminal 13 a. In the present embodiment, the thickness TG1 is one-halfof the thickness TG2. The thickness of the gate coupling portion 13 b isless than the thickness TG2 and equal to the thickness TG1 of the gateframe finger 13 c. In the same manner as the source frame 12, thethickness TG3 of the tie bar portion 13 d is equal to the thickness TG2.Thus, in the gate frame 13, the thickness TG1 of the gate frame finger13 c and the gate coupling portion 13 b and the thickness TG3 of the tiebar portion 13 d are less than the thickness TG2 of the gate terminal 13a. The thickness TG1 of the gate frame finger 13 c and the gate couplingportion 13 b and the thickness TG3 of the tie bar portion 13 d are equalto the thicknesses TD1 and TD3 (see FIG. 5) of the drain frame 11. Thethickness TG2 of the gate terminal 13 a is equal to the thickness TD2 ofthe drain frame 11.

Thus, as viewed in the first direction X, at the portion where the drainframe fingers 11 c overlap the source frame fingers 12 c, at leasteither one of the drain frame fingers 11 c and the source frame fingers12 c are thin. As viewed in the first direction X, the source framefingers 12 c and the gate frame fingers 13 c are both thin at portionswhere thy overlap each other.

As shown in FIG. 8, the transistor 20 is arranged closer to the secondlongitudinal side surface 36 of the encapsulation resin 30. Further, thetransistor 20 is arranged closer to the first longitudinal side surface35 side than the source coupling portion 12 b and the gate couplingportion 13 b. Specifically, a side surface of the transistor 20 closerto the first longitudinal side surface 35 lies at the middle of theencapsulation resin 30 in the second direction Y, and a side surfacecloser to the second longitudinal side surface 36 of the transistor 20is located proximate to the source coupling portion 12 b and the gatecoupling portion 13 b. The transistor 20 is located closer to the secondlongitudinal side surface 36 than the first section 11 m of each drainframe finger 11 c. Portions of the transistor 20 closer to the secondlongitudinal side surface 36 are supported by the second tie barportions 11 i and 11 j.

As can be understood from FIG. 8, the length LFD of the drain framefingers 11P and the length LFDE of the drain frame fingers 11Q aregreater than the length L2 of the transistor 20. The length LFS of thesource frame fingers 12 c is slightly greater than the length L2.

The drain electrode pads 21P and 21Q face front surfaces 11 e of thedrain frame fingers 11P and 11Q in the height direction Z, the sourceelectrode pads 22 face front surfaces 12 e of the source frame fingers12 c in the height direction Z, and the gate electrode pad 23 faces afront surface 13 e of the gate frame finger 13 c in the height directionZ. Each drain electrode pad 21P is electrically connected to thecorresponding drain frame finger 11P. The drain electrode pad 21Q iselectrically connected to the drain frame finger 11Q. Each sourceelectrode pad 22 is electrically connected to the corresponding sourceframe finger 12 c. The gate electrode pad 23 is electrically connectedto the gate frame finger 13 c.

The distance between the adjacent drain frame fingers 11P in the firstdirection X is equal to the distance between the adjacent drainelectrode pads 21P in the first direction X. The width WFD2 of thesecond section 11 n in each drain frame finger 11P is equal to the widthWD of each drain electrode pad 21P. Thus, when the transistor 20 ismounted on the drain frame 11, the drain frame finger 11P entirelycovers the drain electrode pad 21P, and the drain frame finger 11Qentirely covers the drain electrode pad 21Q. Specifically, the edge ofthe distal portion 11 h of the drain frame finger 11P is arranged closerto the second longitudinal side surface 36 than the end of the drainelectrode pad 21P closer to the second longitudinal side surface 36, andthe edge of the drain frame finger 11Q closer to the second longitudinalside surface 36 is arranged at the same position as the end of the drainelectrode pad 21Q closer to the second longitudinal side surface 36.Thus, the drain frame finger 11P is electrically connected to the entiredrain electrode pad 21P, and the drain frame finger 11Q is electricallyconnected to the entire drain electrode pad 21Q. The part of the drainframe finger 11P facing the drain electrode pad 21P in the heightdirection Z includes the distal portion 11 h of the drain frame finger11P and the part of the distal portion 11 h closer to the firstlongitudinal side surface 35. Thus, the drain electrode pad 21P iselectrically connected to the portion of the drain frame finger 11Pexposed from the back surface 32 of the encapsulation resin 30.

The distance between the adjacent source frame fingers 12 c in the firstdirection X is equal to the distance between the adjacent sourceelectrode pads 22 in the first direction X. The width WFS of the sourceframe fingers 12 c is equal to the width WS of the source electrode pads22. Thus, when the transistor 20 is mounted on the source frame 12, eachsource frame finger 12 c entirely covers the corresponding sourceelectrode pad 22. Specifically, the distal portion of each source framefinger 12 c is located closer to the first longitudinal side surface 35than the end of the source electrode pad 22 closer to the firstlongitudinal side surface 35. Thus, the source frame finger 12 c iselectrically connected to the entire source electrode pad 22.

The gate frame finger 13 c covers the entire gate electrode pad 23.Specifically, the distal portion of the gate frame finger 13 c islocated closer to the first longitudinal side surface 35 than the end ofthe gate electrode pad 23 closer to the first longitudinal side surface35. The width WFG of the gate frame finger 13 c is equal to the width WGof the gate electrode pad 23. Thus, the gate frame finger 13 c iselectrically connected to the entire gate electrode pad 23.

As shown in FIGS. 4 to 7, the front surface 11 e of each drain frame 11,the front surface 12 e of each source frame 12, and the front surface 13e of each gate frame 13 are flush with one another. Back surfaces 11 f,12 f, 13 f of the thin portions in the drain frame 11, the source frame12, and the gate frame 13 are located closer to the front surfaces 11 eto 13 e side of the frames 11 to 13 than the back surfaces 11 g, 12 g,and 13 g of the thick portions. Furthermore, as shown in FIGS. 5 to 7,each frame 11 to 13 is arranged closer to the back surface 32 of theencapsulation resin 30 in the height direction Z.

Thus, as shown in FIG. 9, the back surface 11 f of the drain frame 11,the back surface 12 f of the source frame 12, and the back surface 13 fof the gate frame 13 are exposed from the back surface 32 of theencapsulation resin 30. The back surface 11 g of the drain frame 11, theback surface 12 g of the source frame 12, and the back surface 13 g ofthe gate frame 13 shown in FIGS. 5 and 6 are not exposed from the backsurface 32 of the encapsulation resin 30. Specifically, in the sourceframe 12, the three source terminals 12 a are exposed from the backsurface 32 of the encapsulation resin 30. However, the source couplingportion 12 b, the four source frame fingers 12 c, and the tie barportion 12 d are not exposed from the back surface 32. In the gate frame13, the gate terminal 13 a is exposed from the back surface 32 of theencapsulation resin 30. However, the gate coupling portion 13 b, thegate frame finger 13 c, and the tie bar portion 13 d are not exposedfrom the back surface 32. In the drain frame 11, the four drainterminals 11 a, the parts in the drain coupling portion 11 b other thanthe end 11 k, and the base 11 r in the first section 11 m of each of thefive drain frame fingers 11 c and parts other than the distal portion 11h are exposed from the back surface 32 of the encapsulation resin 30. Inthe drain frame 11, the distal portion 11 h and the flanges 11 s of thefirst section 11 m in each of the five drain frame fingers 11 c, and thetie bar portions 11 d, 11 i, and 11 j are not exposed from the backsurface 32. Thus, the width WCDR of the drain coupling portion 11 bexposed from the back surface 32 is smaller than the width WCD of thedrain coupling portion 11 b (see FIG. 3). The width WFDR of the drainframe finger 11 c exposed from the back surface 32 is equal to the widthWFD2 of the second section 11 n (see FIG. 3). The width WCDR is equal tothe width WFD2. The length in the second direction Y of the back surface11 f exposed from the back surface 32 of the encapsulation resin 30 inthe drain frame finger 11 c is equal to the length LFDE of the drainframe finger 11Q.

As shown in FIG. 8, in a region where the drain frame fingers 11 coverlap the source frame fingers 12 c as viewed in the first directionX, the drain frame fingers 11 c are exposed from the back surface 32(see FIG. 9) of the encapsulation resin 30 but the source frame fingers12 c are not exposed from the back surface 32. Thus, the shortestdistance DOY in the second direction Y between each drain frame 11 andthe corresponding source frame 12 where they are exposed from the backsurface 32 of the encapsulation resin 30 is longer than the shortestdistance DIY (see FIG. 8) in the second direction Y between the drainframe 11 and the source frame 12 where they are not exposed from theback surface 32 of the encapsulation resin 30. The shortest distance DOYis the distance in the second direction Y between each drain framefinger 11 c and the corresponding source terminal 12 a. The shortestdistance DIY is the distance in the second direction Y between thedistal end of each drain frame finger 11P and the source couplingportion 12 b.

Furthermore, the shortest distance GOY in the second direction Y betweenthe drain frame 11 and the gate frame 13 exposed from the back surface32 of the encapsulation resin 30 is longer than the shortest distanceGIY (see FIG. 8) in the second direction Y between the drain frame 11and the gate frame 13 where they are not exposed from the back surface32 of the encapsulation resin 30. The shortest distance GOX in the firstdirection X between the gate frame 13 and the source frame 12 exposedfrom the back surface 32 of the encapsulation resin 30 is longer thanthe shortest distance (distance DFgs (see FIG. 3)) in the firstdirection X between the gate frame 13 and the source frame 12 where itis not exposed from the back surface 32 of the encapsulation resin 30.The shortest distance GOY is a distance in the second direction Y of thedrain frame finger 11Q and the gate terminal 13 a. The shortest distanceGOY is equal to the shortest distance DOY. The shortest distance GIY isa distance in the second direction Y of the drain frame finger 11Q andthe gate frame finger 13 c. The shortest distance GOX is the distancebetween the gate terminal 13 a and the adjacent source terminal 12 a.

A method for manufacturing the semiconductor device 1 will now bedescribed.

As shown in FIG. 10, the method for manufacturing the semiconductordevice 1 includes a frame forming process (step S1), a transistormounting process (step S2), a molding process (step S3), and a cuttingprocess (step S4). The manufacturing of the semiconductor device 1 is,for example, performed in the order of the frame forming process, thetransistor mounting process, the molding process, and the cuttingprocess.

In the frame forming process, multiple lead frames 10 are formed fromthe same copper plate that serves as a base material. Each lead frame 10in the frame forming process is connected to the copper plate (basematerial) by the tie bar portions 11 d, 11 i, 11 j, 12 d, and 13 d (seeFIG. 3).

In the transistor mounting process, the transistor 20 is flip-chipmounted on each lead frame 10 (see FIG. 8). Specifically, a solder pasteis applied to the five drain frame fingers 11 c, the four source framefingers 12 c, and the single gate frame finger 13 c of each lead frame10. Bumps made of gold, copper, or the like is formed on the drainelectrode pads 21, the source electrode pads 22, and the gate electrodepad 23 of the transistor 20. The transistor 20 is heated and pressurizedby the lead frame 10 so that the five drain electrode pads 21 face thefive drain frame fingers 11 c, the four source electrode pads 22 facethe four source frame fingers 12 c, and the gate electrode pad 23 facesthe gate frame finger 13 c in the height direction Z. In this manner,the transistor 20 is mounted on the lead frame 10. Thus, each lead frame10 and the transistor 20 are connected without wires such as bondingwires.

In the molding process, the encapsulation resin 30 is molded by, forexample, a mold shaping device. Specifically, the copper plate includingeach lead frame 10, on which the transistor 20 is mounted, is arrangedin a cavity of a mold of the mold shaping device, and the cavity of themold is filled with a molten mold resin (epoxy resin in the presentembodiment).

In the cutting process, each semiconductor device 1 is cut out from thecopper plate. In this case, the tie bar portions 11 d, 11 i, 11 j, 12 d,and 13 d are cut from the copper plate. Thus, the first tie bar portions11 d are exposed from the first lateral side surface 33 and the secondlateral side surface 34 of the encapsulation resin 30. The second tiebar portion 11 i is exposed from the first lateral side surface 33, andthe second tie bar portion 11 j is exposed from the second lateral sidesurface 34. Furthermore, the tie bar portion 12 d is exposed from thefirst lateral side surface 33 of the encapsulation resin 30, and the tiebar portion 13 d is exposed from the second lateral side surface 34. Thesemiconductor device 1 shown in FIG. 1 can be obtained through theprocesses described above.

The semiconductor device 1, which is formed in this manner, can bemounted on the circuit substrate 300 (see FIG. 12) in place of aconventional semiconductor device 200 shown in FIG. 11. In other words,the semiconductor device 1 and the semiconductor device 200 arepin-compatible. In FIG. 11, the back surface of the semiconductor device200 is shown. The circuit substrate 300 is a circuit substrate on whichthe semiconductor device 200 is mounted.

As shown in FIG. 11, the semiconductor device 200 includes a die pad210, a lead frame 220, a transistor 230 mounted on the die pad 210, andan encapsulation resin 240 that encapsulates the transistor 230. Thesemiconductor device 200 has the same package contour as thesemiconductor device 1.

The lead frame 220 includes four drain terminals 221, three sourceterminals 222, and one gate terminal 223 that are connected to the diepad 210. The arrangement of the drain terminals 221, the sourceterminals 222, and the gate terminal 223 is similar to the arrangementof the drain terminals 11 a, the source terminals 12 a, and the gateterminal 13 a (see FIG. 9) of the semiconductor device 1. The sourceterminals 222 and the gate terminal 223 are spaced apart from the diepad 210 in the second direction Y. As shown in FIG. 11, the die pad 210,the four drain terminals 221, the three source terminals 222, and thesingle gate terminal 223 are exposed from a back surface 241 of theencapsulation resin 240.

The transistor 230 is, for example, a vertical Metal Oxide SemiconductorField Effect Transistor (MOSFET) in which the drain electrodes areformed on the back surface (surface faced toward die pad 210) of thetransistor 230, and the source electrodes and the gate electrode areformed on the front surface (surface faced away from die pad 210) of thetransistor 230. The transistor 230 is arranged so that the drainelectrodes are electrically connected to the die pad 210 and so that thesource electrodes and the gate electrode are electrically connected tothe source terminal 222 and the gate terminal 223 by bonding wires (notillustrated) such as aluminum wires.

The die pad 210 is arranged closer to the drain terminals 221 in thesemiconductor device 200, that is, closer to a first longitudinal sidesurface 242 of the encapsulation resin 240. Thus, the transistor 230 isarranged closer to the first longitudinal side surface 242 of theencapsulation resin 240. As shown in FIG. 11, the die pad 210 issubstantially rectangular and exposed from the back surface 241 of theencapsulation resin 240. The length LDP of the die pad 210 in the seconddirection Y is basically equal to the sum of the length LFDE of thedrain frame fingers 11 c exposed from the back surface 32 of theencapsulation resin 30 in the semiconductor device 1 and the width WCDRof the drain coupling portion 11 b (both shown in FIG. 9).

Furthermore, as shown in FIG. 12, a land pattern 301 electricallyconnected to the drain, land patterns 302 electrically connected to thesource, and a land pattern 303 electrically connected to the gate arearranged on the circuit substrate 300. The land pattern 301 is shaped incorrespondence with the die pad 210 of the semiconductor device 200shown in FIG. 11. The land patterns 302 are spaced apart from the landpattern 301 in the second direction Y, and laid out in correspondencewith the source terminals 222. The land pattern 303 and the landpatterns 302 are arranged at corresponding positions in the seconddirection Y. Further, the land pattern 303 is spaced apart from the landpatterns 302 in the first direction X. The land pattern 303 is arrangedat a position corresponding to the gate terminal 223.

As shown in FIG. 12, when applying solder to the land patterns 301 to303 in order to mount the semiconductor device 1 on the circuitsubstrate 300, the land pattern 301 corresponding to the die pad 210 isconnected to the four drain terminals 11 a, the drain coupling portion11 b, and the five drain frame fingers 11 c of the semiconductor device1. The source frame fingers 12 c are not exposed at positions facing theland pattern 301 and thus not electrically connected to the land pattern301. Thus, short-circuiting of the drain and the source can be avoided.The three land patterns 302 are connected to the three source terminals12 a, respectively. The land pattern 303 is connected to the gateterminal 13 a. Thus, the semiconductor device 1 can be mounted on theland patterns 301 to 303 designed in accordance with the semiconductordevice 200, and there is no need to design a new land patterns andmanufacture a new circuit substrate to mount the semiconductor device 1.This avoids cost increases that would occur when manufacturing a newcircuit substrate.

The semiconductor device 1 has the following advantages.

(1) As shown in FIG. 8, the drain frame fingers 11 c of the drain frame11 face the drain electrode pads 21 of the transistor 20 in the heightdirection Z, and the source frame fingers 12 c of the source frame 12face the source electrode pads 22 in the height direction Z. The gateframe finger 13 c of the gate frame 13 faces the gate electrode pads 23of the transistor 20 in the height direction Z. This layout shortens theconnecting distance of between the electrode pads 21 to 23 of thetransistor 20 and the frame fingers 11 c to 13 c. In particular, in thepresent embodiment, the electrode pads 21 of the transistor 20 directlycontact the drain frame fingers 11 c, and the electrode pads 22 directlycontact the source frame fingers 12 c. Thus, the connecting distancebetween the transistor 20 and the lead frame 10 is null.

The connection of the drain frame fingers 11 c and the drain electrodepads 21, the connection of the source frame fingers 12 c and the sourceelectrode pads 22, and the connection of the gate frame finger 13 c andthe gate electrode pad 23 are performed through flip-chip mounting.Thus, bonding wires are not used for the electrical connection of thetransistor 20 and the lead frame 10. This eliminates inductance thatwould be caused by bonding wires. As a result, increases in theinductance of the semiconductor device 1 are limited since bonding wiresare not used.

(2) In the region where the source frame fingers 12 c overlap the drainframe fingers 11 c as viewed in the first direction X, the source framefingers 12 c are not exposed from the back surface 32 of theencapsulation resin 30. In such a configuration, the distance betweenthe drain frame fingers 11 c and the source frame 12 that are exposedfrom the back surface 32 of the encapsulation resin 30 can be increased.Thus, when the semiconductor device 1 is mounted on the circuitsubstrate 300 by the solder paste, for example, connection of the drainframe 11 and the source frame 12 with the solder paste is limited. Thislimits short-circuiting of the drain and the source in the transistor20.

(3) In the region where the drain frame fingers 11 c overlap the sourceframe fingers 12 c as viewed in the first direction X, parts of eachdrain frame finger 11 c other than the distal portion 11 h are exposedfrom the back surface 32 of the encapsulation resin 30. Thus, the heatof the transistor 20 is dissipated to the outside of the semiconductordevice 1 through the drain frame finger 11 c. This improves the heatdissipation performance of the semiconductor device 1.

(4) In the second direction Y, the transistor 20 is arranged closer tothe second longitudinal side surface 36 of the encapsulation resin 30.The length LFS of the source frame fingers 12 c is shorter than thelength LFD of the drain frame fingers 11 c. This limits deformation ofthe source frame fingers 12 c toward the back surface 32 of theencapsulation resin 30 when the transistor 20 is mounted on the sourceframe fingers 12 c. This limits exposure of the source frame fingers 12c from the back surface 32 of the encapsulation resin 30.

In this manner, the source frame fingers 12 c, which are shorter inlength than the drain frame fingers 11 c, are reduced in thickness. Thedeformation amount of each source frame finger 12 c when the transistor20 is mounted on the lead frame 10 would be less than the deformationamount of each drain frame finger when each drain frame finger 11 c isentirely reduced in thickness. This limits exposure of the source framefingers 12 c from the back surface 32 of the encapsulation resin 30 atthe portion where the drain frame fingers 11 c overlap the source framefingers 12 c as viewed in the first direction X.

(5) The source frame fingers 12 c are coupled by the source couplingportion 12 b. This increases the rigidity of each source frame finger 12c. In addition, the distance between the drain frame 11 and the sourceframe 12 can be increased because the source coupling portion 12 b isnot exposed from the back surface 32 of the encapsulation resin 30.Therefore, when the semiconductor device 1 is mounted on the circuitsubstrate 300 using, for example, solder paste, connection of the drainframe 11 and the source frame 12 with the solder paste is limited.

(6) The thickness TD1 of each drain frame finger 11 c is greater thanthe thickness TS1 of each source frame finger 12 c. Thus, when thetransistor 20 is mounted on the drain frame fingers 11 c, deformation islimited in the height direction Z.

In addition, the drain frame fingers 11 c are exposed from the backsurface 32 of the encapsulation resin 30. This easily dissipates theheat of the drain frame 11 and the heat of the transistor 20 to theoutside of the semiconductor device 1 through each drain frame finger 11c. Therefore, the temperature of the semiconductor device 1 does notbecome excessively high. In this manner, the drain frame fingers 11 c,which are longer length than the source frame fingers 12 c, are exposedfrom the back surface 32 of the encapsulation resin 30. This improvesthe heat dissipation performance of the semiconductor device 1 comparedto a configuration in which the drain frame fingers 11 c are not exposedfrom the back surface 32 and the source frame fingers 12 c are exposedfrom the back surface 32.

(7) The drain frame fingers 11 c are coupled to the drain couplingportion 11 b. This increases the rigidity of each drain frame finger 11c. Therefore, when the transistor 20 is mounted on the drain framefingers 11 c, deformation can be further reduced in the height directionZ.

In addition, each drain coupling portion 11 b is exposed from the backsurface 32 of the encapsulation resin 30. Thus, the heat of the drainframe 11 and the heat of the transistor 20 are easily dissipated to theoutside of the semiconductor device 1 through the drain coupling portion11 b. This further ensures that the temperature of the semiconductordevice 1 does not become excessively high.

(8) Each drain frame finger 11P covers the entire surface of thecorresponding drain electrode pad 21P. Thus, the drain frame finger 11Pis electrically connected to the entire surface of the correspondingdrain electrode pad 21P of the transistor 20. Thus, the current suppliedfrom the drain frame 11 to the transistor 20 can be increased. Inaddition, the distal portion 11 h of each drain frame finger 11P is notexposed from the back surface 32 of the encapsulation resin 30. Thus,the distance between each drain frame finger 11P and the source frame 12that are exposed from the back surface 32 of the encapsulation resin 30can be increased. Therefore, when the semiconductor device 1 is mountedon the circuit substrate 300 by, for example, solder paste, connectionof the drain frame 11 and the source frame 12 by the solder paste islimited.

(9) In the portion of each drain frame finger 11 c connected to thecorresponding drain electrode pad 21 of the transistor 20, the partcloser to the first longitudinal side surface 35 is exposed from theback surface 32 of the encapsulation resin 30. Thus, the heat of thetransistor 20 is dissipated to the outside of the semiconductor device 1through the drain electrode pad 21 and the drain frame finger 11 c. Theheat of the transistor 20 is dissipated to the outside of thesemiconductor device 1 over a short path. Thus, the heat of thetransistor 20 is easily dissipated to the outside of the semiconductordevice 1.

(10) The portion of the gate frame finger 13 c overlapping thecorresponding drain frame finger 11 c as viewed in the first direction Xis not exposed from the back surface 32 of the encapsulation resin 30.This increases the distance between the gate frame 13 and the drainframe 11 that are exposed from the back surface 32 of the encapsulationresin 30. Therefore, when the semiconductor device 1 is mounted on thecircuit substrate 300 by, for example, solder paste, connection of thedrain frame 11 and the gate frame 13 by the solder paste is limited.

(11) The length LFG of the gate frame fingers 13 c is less than thelength LFS of the source frame fingers 12 c. This limits deformation ofthe gate frame fingers 13 c toward the back surface 32 of theencapsulation resin 30 when the transistor 20 is mounted on the gateframe finger 13 c. Therefore, exposure of the gate frame fingers 13 cfrom the back surface 32 of the encapsulation resin 30 is limited.

(12) The drain frame fingers 11Q face the gate frame fingers 13 c in thesecond direction Y. Thus, compared to when the drain frame fingers 11Qdo not face the gate frame fingers 13 c in the second direction Y, thatis, when the drain frame fingers 11Q are arranged at positions thatdiffer from the gate frame finger 13 c in the first direction X, thesize of the semiconductor device 1 in the second direction Y can bereduced.

(13) The drain electrode pads 21 and the source electrode pads 22 of thetransistor 20 are alternately arranged in the first direction X. Thus,the distance between each drain electrode pad 21 and the adjacent sourceelectrode pad 22 is decreased in the first direction X. That is, thetravel distance of electrons is decreased between the drain electrodepad 21 and the source electrode pad 22. This increases the switchingspeed of the transistor 20.

The distance between the drain electrode pads 21 adjacent to each otherin the first direction X and the distance between the source electrodepads 22 adjacent to each other in the first direction X are equal. Thus,concentration of the current can be limited at the source electrode pads22 where the distance between the drain electrode pads 21 and the sourceelectrode pads 22 is small in the first direction X when the distance ofthe drain electrode pad 21 and the source electrode pad 22 varies in thefirst direction X.

(14) The drain electrode pad 21Q and the gate electrode pad 23 of thetransistor 20 are aligned in the second direction Y. In other words, thedrain electrode pad 21Q and the gate electrode pad 23 are arranged atcorresponding positions in the first direction X. Thus, compared to whenthe drain electrode pad 21Q and the gate electrode pad 23 are arrangedat different positions in the first direction X, the size of thetransistor 20 in the first direction X can be reduced.

The length LDE of the drain electrode pad 21Q and the length LG of thegate electrode pad 23 are less than the length LD of the drain electrodepad 21P and the length LS of the source electrode pad 22. Thus, comparedto when the length LDE of the drain electrode pad 21Q and the length LGof the gate electrode pad 23 are greater than or equal to the length LDof the drain electrode pad 21P and the length LS of the source electrodepad 22, the size of the transistor 20 in the second direction Y can bereduced.

(15) The thin portions (shaded portions in FIG. 3) of the drain frame11, the source frame 12, and the gate frame 13 are formed through ahalf-etching processing. Thus, compared to other processing methods suchas cutting, the thin portion can easily be formed in the drain frame 11,the source frame 12, and the gate frame 13.

(16) The second tie bar portions 11 i and 11 j are arranged on the drainframe fingers 11P that is closest to the first lateral side surface 33of the drain frame finger 11P and on the drain frame finger 11Q,respectively. In such a configuration, when the transistor 20 is mountedon the lead frame 10, the drain frame fingers 11 c support thetransistor 20 with the second tie bar portions 11 i, 11 j. This limitsdeformation of the drain frame finger 11 c toward the back surface 32 ofthe encapsulation resin 30. Furthermore, the drain frame fingers 11 care supported by of the tie bar portions 11 i and 11 j when the moldresin that molds the encapsulation resin 30 flowed onto the drain framefinger 11 c. This limits curving of the drain frame fingers 11 c.

Furthermore, the drain frame 11 is supported by the first tie barportions 11 d provided on the drain coupling portion 11 b and the secondtie bar portions 11 i and 11 j provided on the drain frame fingers 11 c.This limits tilting of the drain frame 11 when the mold resin that moldsthe encapsulation resin 30 flows onto the drain frame 11.

(17) The width WFD1 of the first section 11 m of each drain frame finger11 c is greater than the width WFD2 of the second section 11 n. Thisincreases the rigidity of the drain frame finger 11 c and limits curvingof the drain frame finger 11 c.

(18) The base 11 r of the first section 11 m of each drain frame finger11 c is exposed from the back surface 32 of the encapsulation resin 30but the flanges 11 s are not exposed from the back surface 32. In such aconfiguration, the surface of each flange 11 s at the side closer to theback surface 32 faces and contacts the encapsulation resin 30. Thus, theflanges 11 s restrict movement of the drain frame finger 11 c toward theback surface 32. This limits projection of the drain frame finger 11 cout of the back surface 32.

(19) Parts of the drain coupling portion 11 b other than the end 11 k isexposed from the back surface 32 of the encapsulation resin 30. The end11 k is not exposed from the back surface 32. In such a configuration,the surface of the end 11 k at the side closer to the back surface 32faces and contacts the encapsulation resin 30. Thus, the end 11 krestricts movement of the drain coupling portion 11 b toward the backsurface 32. This limits projection of the drain coupling portion 11 bout of the back surface 32.

Transistor

The internal structure of the transistor 20 will now be described withreference to FIGS. 13 to 15. The shading in FIG. 14A indicates theregion of a plate film 44, and the shading in FIG. 14B indicates theregion of source electrodes 60.

As shown in FIG. 13, the transistor 20 includes the source electrode 60,a drain electrode 70, a gate electrode 80, and a plate film 44 that arearranged on a group-III nitride semiconductor stacked structure 24serving as a base. As shown in FIG. 14A, the source electrode 60(S), thedrain electrode 70(D), and the gate electrode 80(G) are cyclicallyarranged in the order of SGDGS. Thus, an element structure 25 isconfigured by sandwiching the gate electrode 80 with the sourceelectrode 60 and the drain electrode 70. The plate film 44 is arrangedbetween the gate and the source, and between the drain and the gate. Inthe following description, a plate film 44 arranged between a drain anda gate is referred to as a source field plate 45, and a plate film 44arranged between a gate and a source is referred to as a floating plate46.

The front surface of the group-III nitride semiconductor stackedstructure 24 is divided into an active region 26 that includes theelement structure 25 and a non-active region 27 that excludes the activeregion 26. The non-active region 27 may just be adjacent to the activeregion 26 as shown in FIG. 14A or surround the active region 26 (notshown).

As shown in FIG. 14B, the source electrodes 60 includes a base portion61, which is arranged in the non-active region 27, and source electrodefingers 62, which are integrally connected to the base portion 61. Thesource electrode 60 of the present embodiment is comb-shaped in whichsource electrode fingers 62 extend in a striped manner parallel to oneanother (see FIG. 13). The base portion 61 includes a connection end 63for the source electrode fingers 62 in the non-active region 27. Thesource electrode fingers 62 extend from the connection end 63 toward theactive region 26. That is, the source electrode fingers 62 are arrangedacross the active region 26 and the non-active region 27. In thefollowing description, the direction in which the source electrodefingers 62 extend is referred to as “the third direction V,” and thedirection orthogonal to the third direction V in a plan view of thegroup-III nitride semiconductor stacked structure 24 is referred to as“the fourth direction W.”

A space SP extends between the adjacent source electrode fingers 62 is aregion where the drain electrode 70 is arranged. The drain electrode 70may include a base portion (not shown) in the non-active region 27 and adrain electrode fingers 71 (portion arranged in the space SP), which areintegrally connected to the base portion in the same manner as thesource electrode 60. The drain electrode 70 of the present embodiment iscomb-shaped in which drain electrode fingers 71 extend in a stripedmanner parallel to one another (see FIG. 13). The drain electrodefingers 71 are parallel to the source electrode fingers 62. In thepresent embodiment, the drain electrode finger 71 are arranged in eachspace SP so that the comb-shaped electrode source electrode fingers 62are engaged with the comb-shaped drain electrode fingers 71.

As shown in FIG. 13, the gate electrode 80 surrounds each sourceelectrode finger 62. As shown in FIG. 14A, the gate electrode 80includes a base portion 81 arranged in the non-active region 27 and gateelectrode fingers 82, which are integrally connected to the base portion81. The gate electrode 80 of the present embodiment is comb-shaped inwhich the gate electrode fingers 82 extend in a striped-manner parallelto one another. The base portion 81 includes a connection end 83 for thegate electrode fingers 82 in the non-active region 27. When using aboundary (element separation line 28) of the active region 26 and thenon-active region 27 as a reference, the connection end 83 is locatedtoward an outer side (relatively far side from active region 26) fromthe connection end 63 of the source electrode 60. The gate electrodefingers 82 extend from the connection end 83 toward the active region26. That is, the gate electrode fingers 82 are arranged across theactive region 26 and the non-active region 27. The base portion 81 ofthe gate electrode 80 also includes an extension 84 on the outer sidethan the base portion 61 of the source electrode 60. The extension 84is, for example, a region for forming contact 96 for the gate electrode80.

As shown in FIG. 14A, the source field plate 45 includes a base portion45 a arranged on the non-active region 27 and electrode portions 45 b,which are integrally connected to the base portion 45 a. The sourcefield plate 45 of the present embodiment is arched so that two electrodeportions 45 b extend in the third direction V from the two ends of thebase portion 45 a in the fourth direction W. The source field plate 45,which is arranged closer to the drain electrode finger 71 than the gateelectrode 80, surrounds the drain electrode finger 71 (see FIG. 13). Thebase portion 45 a includes a connection end 45 c for the electrodeportion 45 b in the non-active region 27. When using the elementseparation line 28 as a reference, the connection end 45 c is locatedtoward the outer side from the connection end 63 of the source electrode60. The two electrode portions 45 b extend from the connection end 45 ctoward the active region 26. That is, the two electrode portions 45 bare arranged across the active region 26 and the non-active region 27.When using the element separation line 28 as a reference, the connectionend 45 c may be arranged at a position substantially corresponding tothe position of the connection end 63 of the source electrode 60.

The base portion 61 of each source electrode 60 and the base portion 45a of each source field plate 45 are partially overlapped in thenon-active region 27. In the overlapping portion, the source electrode60 and the source field plate 45 are connected by source contacts 29.The source contact 29 is, for example, arranged at positions facing thespace SP (positions avoiding source electrode finger 62 of sourceelectrode 60).

The floating plate 46 includes a base portion 46 a, which is arranged inthe non-active region 27, and electrode portions 46 b, which areintegrally connected to the base portion 46 a. The floating plate 46 ofthe present embodiment is arched so that two electrode portions 46 bextend in the third direction V from the ends of the base portion 46 ain the fourth direction W. The floating plate 46 is arranged closer tothe source electrode finger 62 than the gate electrode 80, surrounds thesource electrode finger 62 (see FIG. 13). The base portion 46 a includesa connection end 46 c for the electrode portion 46 b in the non-activeregion 27. When using the element separation line 28 as a reference, theconnection end 46 c is located toward the outer side from the connectionend 63 of the source electrode 60 and the connection end 45 c of thesource field plate 45. The two electrode portions 46 b extended from theconnection end 46 c toward the active region 26. That is, the twoelectrode portions 46 b extend across the active region 26 and thenon-active region 27. When using the element separation line 28 as areference, the connection end 46 c may be arranged at a positionsubstantially corresponding to the connection end 63 of the sourceelectrode 60 or the connection end 45 c of the source field plate 45.

As shown in FIG. 13, source wires 91, drain wires 92, and gate wires 93are electrically connected to the source electrodes 60, the drainelectrodes 70, and the gate electrodes 80, respectively. Specifically,contacts 94, 95, 96 are formed so as to reach each of the sourceelectrode 60, the drain electrode 70, and the gate electrode 80 in aninsulating layer 90 applied to an insulating layer 50 (both shown inFIG. 15) where the source electrode 60, the drain electrode 70, and thegate electrode 80 are formed. The source wires 91, the drain wires 92,and the gate wires 93 are connected to the source electrodes 60, thedrain electrodes 70, and the gate electrodes 80 by the contacts 94, 95,96. The source wires 91, the drain wires 92, and the gate wires 93 areelectrically connected to the source electrode pads 22, the drainelectrode pads 21, and the gate electrode pads 23, respectively.

Plural groups of the contact 94 (hereinafter referred to as “the groupsof contacts 94”) that connect the source electrode 60 and the sourcewire 91 are arranged on each source electrode finger 62 in the thirddirection V. The plural (four in the present embodiment) groups ofcontacts 94 are spaced apart from one another at a certain interval inthe third direction V. The groups of contacts 94 at the two ends in thethird direction V have fewer contacts 94 than the other group ofcontacts 94. Plural groups of contacts 95 (hereinafter referred to as“the groups of contacts 95”) that connect the drain electrode 70 and thedrain wire 92 are arranged on each drain electrode finger 71 in thethird direction V. The plural (three in the present embodiment) groupsof contacts 95 are spaced apart from one another at a certain intervalin the third direction V. Plural groups of the contacts 96 (hereinafterreferred to as “the groups of contacts 96”) that connect the gateelectrode 80 and the gate wire 93 are arranged in the fourth direction Won the extensions 84 at the two ends of the group-III nitridesemiconductor stacked structure 24. The plural groups of contacts 96 arespaced apart from one another at a certain interval in the fourthdirection W. The groups of contacts 96 are arranged at positionscorresponding to the positions of the source electrode finger 62 and thegate electrode finger 82 in the fourth direction W.

The source wires 91, the drain wires 92, and the gate wires 93 eachextend in the fourth direction W. The source wires 91 and the drainwires 92 extend across the source electrode fingers 62 and the drainelectrode fingers 71 in the fourth direction W. The source wires 91 andthe drain wires 92 are alternately arranged in the third direction V.The gate wires 93 are located outward (toward non-active region 27) fromthe source electrode fingers 62 of the source electrodes 60 and thedrain electrode fingers 71 of the drain electrodes 70 in the thirddirection V. The source wires 91 located at the outermost side (side ofnon-active region 27) in the third direction V of the plurality ofsource wire 91 (hereinafter may also be referred to as “the source wires91 at the outer sides”) are adjacent to the gate wires 93 in the thirddirection V. The source wires 91 at the outer sides cover each sourceelectrode finger 62 of the source electrodes 60 in the third direction Vand also cover part of the non-active region 27.

The number of source wires 91 is greater than the number of drain wires92. The source wires 91 at the outer sides each have a width (widthdimension in the third direction V) that is smaller than the width ofthe other source wires 91. The width of the other source wires 91 isequal to the width of the drain wires 92 (width dimension in the thirddirection V). The gate wires 93 each have a width (width dimension inthe third direction V) that is smaller than the widths of the sourcewires 91 and the drain wires 92.

The width, shape, and number of the source wires 91, the drain wires 92,and the gate wires 93 may be set in any manner. For example, the numberof the source wires may be equal 91 to the number of the drain wires 92.

As shown in FIG. 15, the group-III nitride semiconductor stackedstructure 24 includes a substrate 40, a buffer layer 41 formed on thefront surface of the substrate 40, an electron travel layer 42epitaxially grown on the buffer layer 41, and an electron supply layer43 epitaxially grown on the electron travel layer 42. A back electrode59 is formed on a back surface of the substrate 40. The back electrode59 is electrically connected to the source electrode 60 to function as asource potential.

The substrate 40 is, for example, a conductive silicon substrate thathas, for example, an impurity concentration of 1×10¹⁷ cm⁻³ to 1×10²⁰cm⁻³ (more specifically, about 1×10¹⁸ cm⁻³).

The buffer layer 41 is, for example, a multi-layered buffer layer inwhich a first buffer layer 41 a and a second buffer layer 41 b arestacked one after another. The first buffer layer 41 a is in contactwith the front surface of the substrate 40. The second buffer layer 41 bis applied to a front surface of the first buffer layer 41 a (surface onopposite side of substrate 40). The first buffer layer 41 a is, forexample, configured by an AlN film and has a film thickness of, forexample, about 0.2 μm. The second buffer layer 41 b is, for example,configured by an AlGaN film and has a film thickness of, for example,about 0.2 μm.

The electron travel layer 42 and the electron supply layer 43 include agroup-III nitride compound semiconductor (hereinafter simply referred toas “nitride semiconductor”) having different Al compositions. Theelectron travel layer 42 includes, for example, a GaN layer and has athickness of, for example, about 0.5 μm. The electron supply layer 43includes, for example, a Al_(x)Ga_(1-x)N layer (0<x<1) and has athickness of, for example, greater than or equal to 5 nm and less thanor equal to 30 nm (more specifically, about 20 nm).

In this manner, the electron travel layer 42 and the electron supplylayer 43 include nitride semiconductors having different Al compositionsand form a hetero junction, in which a lattice mismatch occurs inbetween. Due to the polarization caused by the hetero junction and thelattice mismatch, a two-dimensional electron gas 47 spreads at aposition close to the interface of the electron travel layer 42 and theelectron supply layer 43 (e.g., position located at a distance of abouta few A from the interface).

In the electron travel layer 42, for example, a shallow donor levelE_(D), a deep donor level E_(DD), a shallow acceptor level E_(A), and adeep acceptor level E_(DA) are formed in terms of an energy bandstructure.

The shallow donor level E_(D) is, for example, an energy level at aposition spaced apart by 0.025 eV or less from an energy level E_(C) ofa lower end (bottom) of a conduction band of the electron travel layer42 and may simply be referred to as “the donor level E_(D)” if it can bedistinguished from the deep donor level E_(DD). Normally, the electronof the donor doped at this position is excited by the conduction bandeven at a room temperature (about heat energy kT=0.025 eV) and becomes afree electron. The impurities doped to the electron travel layer 42including the GaN layer to form the shallow donor level E_(D) include,for example, at least one type of Si or O. The deep donor level E_(DD)is, for example, an energy level at a position spaced apart by 0.025 eVor greater from the energy level E_(C) of the lower end (bottom) of theconduction band of the electron travel layer 42. That is, the deep donorlevel E_(BB) is formed by doping a donor in which an ionization energynecessary for excitation is greater than the heat energy of the roomtemperature. Therefore, normally, the electron of the donor doped atthis position is not excited by the conduction band at room temperatureand is in a state captured by the donor.

The shallow acceptor level E_(A) is, for example, an energy level at aposition spaced apart by 0.025 eV or less from the energy level E_(v) ofan upper end (top) of a valence electron of the electron travel layer 42and may simply be referred to as “the acceptor level E_(A)” if it can bedistinguished from the deep acceptor level E_(DA). Normally, a hole ofthe acceptor doped to the relevant position is excited by a valence bandeven at room temperature (about heat energy kT=0.025 eV) and becomes afree hole. The deep acceptor level E_(DA) is, for example, an energylevel at a position spaced apart by greater than or equal to 0.025 eVfrom the energy level E_(v) of the upper end (top) of the valenceelectron of the electron travel layer 42. That is, the deep acceptorlevel E_(DA) is formed by doping an acceptor in which the ionizationenergy necessary for excitation is greater than the heat energy of theroom temperature. Therefore, normally, the hole of the acceptor doped atthis position is not excited by the valence band at room temperature andis in a state captured by the acceptor. The impurities doped in theelectron travel layer 42 including the GaN layer for forming the deepacceptor level E_(DA) includes, for example, at least one type selectedfrom a group consisting of C, Be, Cd, Ca, Cu, Ag, Sr, Ba, Li, Na, K, Sc,Zr, Fe, Co, Ni, Ar, and He.

In the present embodiment, the concentrations of the impurities (dopant)that form the shallow donor level E_(D), the deep donor level E_(DD),the shallow acceptor level E_(A), and the deep acceptor level E_(DA)described above is referred to as the shallow donor concentration N_(D),the deep donor concentration N_(DD), the shallow acceptor concentrationN_(A), and the deep acceptor concentration N_(DA). For example, if onlyC (carbon) is doped to the electron travel layer 42 at a concentrationof 0.5×10¹⁶ cm⁻³ as the impurity for forming the deep acceptor levelE_(DA), the carbon concentration is defined as the deep acceptorconcentration N_(DA). Such concentrations N_(B), N_(DD), N_(A), andN_(DA) can be measured through, for example, Secondary Ion MassSpectrometry (SIMS).

The impurity concentration for the entire electron travel layer 42 ispreferably N_(A)+N_(BA)−N_(D)− N_(DD)>0. This inequality equation meansthat the sum (N_(A)+N_(BA)) of the impurity concentrations of anacceptor atom that can capture the released electron is greater than thesum (N_(D)+N_(DD)) of the impurity concentrations of a donor atom thatcan release the electron. That is, in the electron travel layer 42,substantially all of the electrons released from the shallow donor atomand the deep donor atom are captured by the shallow acceptor atom or thedeep acceptor atom without being excited by the conduction band. Thus,the electron travel layer 42 is a semi-insulating i-type GaN.

In the present embodiment, for example, the shallow donor concentrationN_(D) is greater than or equal to 1×10¹⁶ cm⁻³ and less than or equal to1×10¹⁷ cm⁻³, and the deep donor concentration N_(DD) is greater than orequal to 1×10¹⁶ cm⁻³ and less than or equal to 1×10¹⁷ cm⁻³. The shallowacceptor concentration N_(A) is greater than or equal to 1×10¹⁶ cm⁻³ andless than or equal to 5×10¹⁶ cm⁻³, and the deep acceptor concentrationN_(BA) is greater than or equal to 1×10¹⁶ cm³ and less than or equal to1×10¹⁸ cm⁻³.

The electron supply layer 43 includes, for example, an AlN layer havinga thickness of about a few atomic thickness (less than or equal to 5 nm,preferably greater than or equal to 1 nm and less than or equal to 5 nm,more preferably greater than or equal to 1 nm and less than or equal to3 nm) at the interface of the electron supply layer 43 and the electrontravel layer 42. Such an AlN layer limits the scattering of electronsand contributes to improving the electron mobility.

An oxide film 48 is selectively formed on the front surface of theelectron supply layer 43 extending to the electron travel layer 42. Theoxide film 48 has a film thickness substantially equal to the electronsupply layer 43. The oxide film 48 is, for example, a thermal oxidefilm, and formed without damaging the interface of the oxide film 48 andthe electron travel layer 42. When the electron supply layer 43 is theAlN layer, the oxide film 48 may include an AlON film.

Furthermore, the transistor 20 further includes a ground layer 49 and aninsulating layer 50 formed on the group-III nitride semiconductorstacked structure 24.

The ground layer 49 is formed on the entire front surface of thegroup-III nitride semiconductor stacked structure 24 including formingregions of the drain electrode 70 and the source electrode 60. Theground layer 49 includes, for example, a SiN film, and has a thicknessof, for example, greater than or equal to 5 nm and less than or equal to200 nm.

The insulating layer 50 covers the ground layer 49 and includes a firstlayer 50 a and a second layer 50 b, which is formed on the first layer50 a. For example, the first layer 50 a and the second layer 50 b bothinclude a SiO₂ film. The insulating layer 50 has a thickness of, forexample, 1.5 μm or greater and 2 μm or less. Individually, the firstlayer 50 a has a thickness of, for example, 500 nm or greater and 1000nm or less, and the second layer 50 b has a thickness of, for example,500 nm or greater and 1000 nm or less.

The first layer 50 a and the ground layer 49 include gate openings 51that extend to the group-III nitride semiconductor stacked structure 24.The oxide film 48 is exposed at the bottom of each gate opening 51. Agate insulating film 52 is formed in each gate opening 51 so as to coverthe bottom and side of the gate opening 51. The gate insulating film 52is also formed between the first layer 50 a and the second layer 50 b inaddition to the inside of the gate opening 51. The gate insulating film52 includes a material film of at least one type selected from a groupconsisting of, for example, Si, Al, and Hf as a constituent element.Specifically, the gate insulating film 52 includes a material film of atleast one type selected from a group consisting of SiN, SiO₂, SiON,Al₂O₃, AlN, AlON, HfSiO, HfO₂, and the like. Preferably, the gateinsulating film 52 includes the Al₂O₃ film. The gate insulating film 52has a thickness of, for example, 10 nm of greater and 100 nm or less.

The gate electrode 80 is buried in the gate opening 51. The gateelectrode 80 includes, for example, an overlap portion 85 formed on thegate insulating film 52 at a peripheral edge of the gate opening 51. Thegate electrode 80 may be filled in the gate opening 51 so as not tobulge project upward from the open end of the gate opening 51. The gateelectrode 80 may be made from, for example, a metal electrode of Mo, Ni,and the like, or may be made from a semiconductor electrode of dopedpolysilicon, and the like. Since the metal electrode has buryingproperties that are inferior to polysilicon, the overlap portion 85 canbe easily formed when the metal electrode is used.

The source field plate 45 and the floating plate 46 are arranged besidethe gate electrode 80 so as to partially form the side of the gateopening 51. Specifically, the source field plate 45 and the floatingplate 46 are formed by the insulating layer 53 on the ground layer 49 soas to be exposed toward the inside of the gate opening 51 at the lowerpart of the side of the gate opening 51. That is, the side of the gateopening 51 includes a stacked interface of a conductive layer/insulatinglayer in which the lower side is formed by the source field plate 45 andthe floating plate 46 and the upper side is formed by the insulatinglayer 50 (first layer 50 a).

An insulative side wall 54 is formed at the side of the gate opening 51so as to contact the source field plate 45 and the floating plate 46.That is, the side wall 54 is arranged between the side of the gateopening 51 and the gate insulating film 52. The side wall 54 includes amaterial film of at least one type selected from a group consisting of,for example, SiO₂, SiN, and SiON. Preferably, the side wall 54 includesthe SiO₂ film. The side wall 54 has a thickness of, for example, 10 nmor greater and 200 nm or less.

The source field plate 45 and the floating plate 46 are insulated fromthe gate electrode 80 by the side wall 54 and the gate insulating film52. The distance DPgf from the gate electrode 80 to the source fieldplate 45 and the floating plate 46 in the fourth direction W is, forexample, 1 μm, and preferably 50 nm or greater and 200 nm or less. Thedistance DPgf of the present embodiment is defined by the total of thethicknesses of the gate insulating film 52 and the side wall 54. If theside wall 54 is omitted, the distance DPgf is defined by the thicknessof the gate insulating film 52. The relationship of the length Lfp ofthe source field plate 45 in the fourth direction W and the distanceDPgd between the gate electrode 80 and the drain electrode 70 in thefourth direction W satisfies Lfp<1/3 DPgd. When a withstanding pressureof the semiconductor device 1 is less than or equal to 200 V, the lengthLfp is, for example, 0.25 μm or greater and 1.5 μm or less, and thedistance DPgd is, for example, 1 μm or greater and 6 μm or less. Thesource field plate 45 and the floating plate 46 include, for example, anMo film, and has a thickness of, for example, 10 nm or greater and 200nm or less.

The insulating layer 50 and the ground layer 49 includes a sourcecontact hole 55 and a drain contact hole 56 that extend to the group-IIInitride semiconductor stacked structure 24. The source contact hole 55and the drain contact hole 56 are formed at positions spaced apart inthe lateral direction (fourth direction W) from the gate opening 51. Thesource electrode 60 and the drain electrode 70 are buried in the sourcecontact hole 55 and the drain contact hole 56, respectively. The sourceelectrode 60 and the drain electrode 70 are respectively electricallyconnected to the group-III nitride semiconductor stacked structure 24 inthe source contact hole 55 and the drain contact hole 56.

The source contact hole 55 and the drain contact hole 56 each includeohmic contact openings 57 and 58 that are relatively larger than theinsulating layer 50 in the ground layer 49. The source electrode 60 andthe drain electrode 70 each include ohmic electrodes 64 and 72, whichare located in the ohmic contact openings 57 and 58, and pad electrodes65 and 73, which are located in the insulating layer 50. The ohmicelectrodes 64 and 72 have ends in the third direction V of the space SP(see FIG. 14A) located at the corresponding positions but, for example,the end of the ohmic electrode 72 on the drain side may be selectivelylocated toward the rear. The pad electrodes 65 and 73 are formed on theohmic electrodes 64 and 72 with their tops exposed from the frontsurface of the insulating layers 50. The ohmic electrodes 64 and 72 andthe pad electrodes 65 and 73 each include, for example, a Ti/Al film.

Although shown in a cross section that differs from the position shownin FIG. 15, the insulating layer 50 includes a contact hole 50 c thatextends to the source field plate 45. The source contact 29 is buried inthe contact hole 50 c. The source field plate 45 and the source contact29 are thereby electrically connected.

As shown in FIG. 15, the source wire 91 includes a first wire 91 aformed on the insulating layer 50 and a second wire 91 b formed on theinsulating layer 90. The first wire 91 a is electrically connected tothe source electrode 60 through a contact 94 extending to the sourceelectrode 60 in the insulating layer 50. The second wire 91 b iselectrically connected to the source electrode pad 22 (see FIG. 2). Thesecond wire 91 b is electrically connected to the first wire 91 athrough a contact hole 90 a extending to the first wire 91 a in theinsulating layer 90. Although not shown in FIG. 15, the drain wire 92and the gate wire 93 (both shown in FIG. 13) are also formed on theinsulating layer 50 and the insulating layer 90 in the same manner asthe source wire 91.

According to the transistor 20, the electron supply layer 43 having adifferent Al composition is formed on the electron travel layer 42 toform the hetero junction, as described above. Thus, the two-dimensionalelectron gas 47 is thereby formed in the electron travel layer 42 nearthe interface of the electron travel layer 42 and the electron supplylayer 43, and the HEMT using the two-dimensional electron gas 47 as achannel is formed. The gate electrode 80 faces the electron travel layer42 with the stacked film of the oxide film 48 and the gate insulatingfilm 52 in between, and the electron travel layer 42 does not existimmediately below the gate electrode 80. Therefore, the two-dimensionalelectron gas 47 resulting from the polarization caused by the latticemismatch of the electron supply layer 43 and the electron travel layer42 is not formed immediately below the gate electrode 80. Thus, when abias is not applied (at time of zero bias) to the gate electrode 80, thechannel formed by the two-dimensional electron gas 47 is shielded atimmediately below the gate electrode 80. The normally OFF type HEMT isrealized in such a manner. When an appropriate ON voltage (e.g., 5 V) isapplied to the gate electrode 80, the channel is induced into theelectron travel layer 42 immediately below the gate electrode 80, andthe two-dimensional electron gas 47 on both sides of the gate electrode80 is connected. This connects the source and the drain.

During use, a predetermined voltage (e.g., greater than or equal to 200V and less than or equal to 400 V) at which the drain electrode 70becomes positive, for example, is applied between the source electrode60 and the drain electrode 70. In such a state, the OFF voltage (0 V) orthe ON voltage (5 V) is applied to the gate electrode 80 using thesource electrode 60 as a reference potential (0 V).

The interface of the oxide film 48 and the electron travel layer 42 iscontinuous with the interface of the electron supply layer 43 and theelectron travel layer 42, and the state of the interface of the electrontravel layer 42 immediately below the gate electrode 80 is the same asthe state of the interface of the electron supply layer 43 and theelectron travel layer 42. Thus, the electron mobility in the electrontravel layer 42 immediately below the gate electrode 80 is held in ahigh state.

The transistor 20 of the present embodiment has the followingadvantages.

(20) The transistor 20 includes the source field plate 45 electricallyconnected to the source electrode 60 arranged between the gate and thedrain. Thus, a gate field plate extending in the lateral direction(fourth direction W) on the gate insulating film 52 integrally from thegate electrode 80 is not needed. Thus, the capacitance between the gateand the drain can be reduced. As a result, the parasitic capacitance ofthe transistor 20 can be reduced. Thus, high speed switching operation,high frequency operation, and the like can be realized.

(21) The gate electrode 80 includes the side wall 54 that contacts thesource field plate 45 and the floating plate 46. The gate insulatingfilm 52 is formed so as to cover the side wall 54. Thus, the distancefrom the gate electrode 80 to the source field plate 45 and the floatingplate 46 can be controlled mainly by the thickness of the side wall 54.Thus, the thickness of the gate insulating film 52 can be mainlydesigned in accordance with the intended gate threshold value voltage.

(22) The distance DPgf between the gate electrode 80, and the sourcefield plate 45 and the floating plate 46 is less than or equal to 1 μm.According to such a configuration, the source field plate 45 and thefloating plate 46 are arranged relatively close to the gate electrode80, and thus the electric field concentration at each end of the sourcefield plate 45 and the floating plate 46 can be lowered in asatisfactory manner.

(23) The relationship of the length Lfp of the source field plate 45 andthe distance DPgd between the gate electrode 80 and the drain electrode70 satisfies Lfp<1/3 DPgd. According to such a configuration, the areaof the source field plate 45 is relatively small so that the increase incapacitance between the drain and the source caused by the source fieldplate 45 can be limited.

(24) The conductive structure electrically connected to each of thesource electrode 60 and the source field plate 45 across the upper sideof the gate electrode 80 does not need to be arranged in the activeregion 26 as a structure for electrically connecting the sourceelectrode 60 and the source field plate 45 by arranging the sourcecontact 29 in the non-active region 27. When such a conductive structureis arranged in the active region 26, this may become a factor forincreasing the parasitic capacitance of the semiconductor device 1.However, increases in the parasitic capacitance are limited byconnecting the source electrode 60 and the source field plate 45 in thenon-active region 27 as described above.

(25) The transistor 20 includes the electron travel layer 42 and theelectron supply layer 43 that form the hetero junction. The electronsupply layer 43 selectively includes the oxide film 48 at the bottom ofthe gate opening 51. According to such a configuration, thetwo-dimensional electron gas 47 immediately below the gate electrode 80can be reduced, and thus a normally OFF type HMET can be realized.

(26) An asymmetric structure in which the distance between the gateelectrode finger 82 and the drain electrode finger 71 is longer than thedistance between the gate electrode finger 82 and the source electrodefinger 62 is obtained. Thus, excessive increases are limited in theelectric field generated between the gate electrode finger 82 and thedrain electrode finger 71. This allows the withstanding pressure of thetransistor 20 to be increased.

[DC/DC Converter]

The semiconductor device 1 described above can be applied to a DC/DCconverter. The DC/DC converter can be applied to, for example, a powersupply circuit for supplying power to a CPU, a primary side circuit in acontactless power supply, and the like.

FIG. 16 is an example of the DC/DC converter, and shows a configurationof a chopper type DC/DC converter 100 that lowers and outputs an inputvoltage from an external power supply (not shown). The DC/DC converter100 is driven at 30 MHz.

The DC/DC converter 100 includes the semiconductor device 1, a coil 101,a diode 102, a capacitor 103, and a control circuit 110. The drain(drain terminal 11 a) of the semiconductor device 1 is electricallyconnected to the external power supply. A first end 101 a of the coil101 is electrically connected to the source (source terminal 12 a) ofthe semiconductor device 1. A cathode of the diode 102 is electricallyconnected between the drain of the semiconductor device 1 and the firstend 101 a of the coil 101, and an anode of the diode 102 is grounded.One side of the capacitor 103 is electrically connected to a second end101 b of the coil 101, and the other side of the capacitor 103 isgrounded.

The control circuit 110 is electrically connected to the gate of thesemiconductor device 1 (gate terminal 13 a). The control circuit 110 iselectrically connected to a connection point of the second end 101 b ofthe coil 101 and the capacitor 103. The control circuit 110 detects thevoltage at the connection point of the second end 101 b of the coil 101and the capacitor 103 and outputs a gate signal of the semiconductordevice 1 based on the detected voltage.

Second Embodiment

A configuration of the semiconductor device 1 of a second embodimentwill be described with reference to FIGS. 17 and 18. The semiconductordevice 1 of the present embodiment differs from the semiconductor device1 of the first embodiment in the configuration of part of the sourceframe 12. In the following description, same reference numerals aredenoted on the configuring elements same as the configuration of thesemiconductor device 1 of the first embodiment, and the descriptionthereof will be omitted.

As shown in FIG. 17, in the source frame 12, the length LFS of thesource frame fingers 12 c is shorter than the length LFS of the sourceframe fingers 12 c of the first embodiment (see FIG. 3). The length LFSis greater than the length LFG of the gate frame finger 13 c. In thesecond direction Y, the distal end of each source frame finger 12 c islocated closer to the second longitudinal side surface 36 of theencapsulation resin 30 than the second tie bar portions 11 i and 11 j ofthe drain frame finger 11 c.

The length LFS can be set to any length within a range shorter than thelength LFS (see FIG. 3) of the source frame finger 12 c of the firstembodiment and a length that allows for electrical connection to thesource electrode pad 22. In one example, in the second direction Y, thedistal end position of the source frame finger 12 c may be the locatedat a position corresponding to the distal end position of the drainframe finger 11Q. In other words, as viewed in the first direction X,the source frame finger 12 c may be overlapped with only the distalportion 11 h (shaded portion of the drain frame finger 11P in FIG. 17)of the drain frame finger 11P. Thus, in the region where the drain framefingers 11P are overlapped with the source frame fingers 12 c in thefirst direction X, the drain frame fingers 11P and the source framefingers 12 c are both not exposed from the back surface 32 (see FIG. 9)of the encapsulation resin 30. In another example, the length LFS may beequal to the length LFG.

As shown in FIG. 18, when the transistor 20 is mounted on the lead frame10, the distal end of each source frame finger 12 c is located slightlycloser to the second longitudinal side surface 36 than the end of eachsource electrode pad 22 of the transistor 20 located closer to the firstlongitudinal side surface 35 of the encapsulation resin 30 in the seconddirection Y. In other words, the portion in the source electrode pad 22that is closer to the second longitudinal side surface 36 faces thesource frame finger 12 c in the height direction Z, and the end closerto the first longitudinal side surface 35 in the source electrode pad 22does not face the source frame finger 12 c in the height direction Z.Thus, the portion closer to the second longitudinal side surface 36 ofthe source electrode pad 22 is electrically connected to the sourceframe finger 12 c. In other words, the source frame finger 12 c ispartially connected to the source electrode pad 22.

The semiconductor device 1 of the present embodiment has the followingeffects.

(27) The distal end of each source frame finger 12 c is located closerto the second longitudinal side surface 36 than the end of each sourceelectrode pad 22 in the transistor 20 located closer to the firstlongitudinal side surface 35 of the encapsulation resin 30. Since thelength LFS of the source frame finger 12 c is short, the rigidity of thesource frame finger 12 c can be improved. Therefore, when the transistor20 is mounted on the source frame finger 12 c, deformation of the sourceframe finger 12 c is limited while maintaining the electrical connectionof the source frame finger 12 c and the source electrode pad 22.Therefore, exposure of the source frame finger 12 c is limited from theback surface 32 of the encapsulation resin 30.

Third Embodiment

A configuration of the semiconductor device 1 of a third embodiment willnow be described with reference to FIGS. 19 to 21. The semiconductordevice 1 of the present embodiment differs from the semiconductor device1 of the first embodiment in that a heat dissipation plate 130 is added.In the following description, same reference numerals are denoted on theconfiguring elements same as the configuration of the semiconductordevice 1 of the first embodiment, and the description thereof will beomitted.

As shown in FIG. 19, the heat dissipation plate 130 is exposed from thefront surface 31 of the encapsulation resin 30. The heat dissipationplate 130 exposed from the front surface 31 is rectangular and elongatedso that the longitudinal direction is the first direction X. Preferably,the heat dissipation plate 130 is located toward the second longitudinalside surface 36 (toward source terminal 12 a and gate terminal 13 a) ofthe encapsulation resin 30. The heat dissipation plate 130 is made froma metal material having superior heat dissipation properties, such as,for example, copper and aluminum.

As shown in FIG. 20, the heat dissipation plate 130 includes a cover 131that covers the back surface 20 b of the transistor 20, a clip 132 thatis connected to the source frame 12, and a coupling portion 133 thatcouples the cover 131 and the clip 132. The cover 131, the clip 132, andthe coupling portion 133 are formed by, for example, the same member.

The cover 131 is rectangular in a plan view. The cover 131 covers theentire back surface 20 b of the transistor 20. The cover 131 iselectrically connected to the back electrode 59 (see FIG. 15) of thetransistor 20. Thus, the cover 131 functions as a source potential. Asshown in FIG. 19, the cover 131 includes a portion exposed from thefront surface 31 of the encapsulation resin 30. As shown in FIG. 21, thecover 131 is in contact with the back surface 20 b of the transistor 20.

The cover 131 may have any shape in a plan view. For example, the shapeof the cover 131 may be substantially rectangular in which the fourcorners of the cover 131 are rounded. Alternatively, the cover 131 maybe elliptical in which the long axis extends in the first direction X.Furthermore, the cover 131 may partially cover the back surface 20 b ofthe transistor 20. The cover 131 need only partially cover the backsurface 20 b of the transistor 20.

As shown in FIG. 20, the clip 132 extends in the first direction X. Thelength LH2 of the clip 132 in the first direction X is shorter than thelength LH1 of the cover 131 in the first direction X. As shown in FIG.21, the clip 132 is located closer to the second longitudinal sidesurface 36 of the encapsulation resin 30 than the cover 131 in thesecond direction Y. Further, the clip 132 is located closer to the leadframe 10 than the cover 131 in the height direction Z. The clip 132 isin contact with the source coupling portion 12 b of the source frame 12.In other words, the clip 132 is electrically connected to the sourceframe 12. The clip 132 is not in contact with the gate frame 13.

As shown in FIG. 20, the coupling portion 133 extends from the end faceof the cover 131 located closer to the clip 132 toward the clip 132. Thelength LH3 of the coupling portion 133 in the first direction X is equalto the length LH2 of the clip 132. As shown in FIG. 21, the couplingportion 133 is inclined toward the lead frame 10 (back surface 32) fromthe cover 131 toward the second longitudinal side surface 36. The clip132 may be omitted from the heat dissipation plate 130. Alternatively,the clip 132 and the coupling portion 133 may be omitted from the heatdissipation plate 130.

The semiconductor device 1 of the present embodiment has the followingadvantages.

(28) The semiconductor device 1 includes the heat dissipation plate 130.Thus, the heat of the transistor 20 is easily dissipated to the outsideof the semiconductor device 1 through the heat dissipation plate 130.Therefore, the temperature of the transistor 20 does not becomeexcessively high.

(29) The cover 131 of the heat dissipation plate 130 covers the entireback surface 20 b of the transistor 20. Thus, compared to when the heatdissipation plate partially covers the back surface 20 b of thetransistor 20, the heat of the transistor 20 is easily dissipated to theoutside of the semiconductor device 1. This further ensures that thetemperature of the transistor 20 does not become excessively high.

Fourth Embodiment

A configuration of the semiconductor device 1 of a fourth embodimentwill now be described with reference to FIGS. 22 and 23. Thesemiconductor device 1 of the present embodiment differs from thesemiconductor device 1 of the first embodiment in the shape of the drainframe 11. In the following description, same reference numerals aredenoted on the configuring elements same as the configuration of thesemiconductor device 1 of the first embodiment, and the descriptionthereof will be omitted.

As shown in FIG. 22, the width WCD of the drain coupling portion 11 b ofthe drain frame 11 is greater than the width WCD of the drain couplingportion 11 b of the first embodiment (see FIG. 3). In the seconddirection Y, a gap is formed between an edge of the drain couplingportion 11 b located closer to the second longitudinal side surface 36of the encapsulation resin 30 and an edge of the transistor 20 closer tothe first longitudinal side surface 35 of the encapsulation resin 30.The size of the width WCD of the drain coupling portion 11 b can bechanged.

When the width WCD of the drain coupling portion 11 b is increased, thelength LFD of the drain frame finger 11P becomes less than the lengthLFD of the drain frame fingers 11P of the first embodiment (see FIG. 3),and the length LFDE of the drain frame finger 11Q becomes less than thelength LFDE of the drain frame finger 11Q of the first embodiment (seeFIG. 3). The length LFD of the drain frame fingers 11P in the presentembodiment is greater than the length LFS of the source frame fingers 12c, and the length LFDE of the drain frame finger 11Q is shorter than thelength LFS. In the present embodiment, the length of the second section11 n is not changed, and the length of the first section 11 m isdecreased. The length LFD can be changed. For example, the length LFDmay be equal to the length LFS.

The two ends 11 t of the drain coupling portion 11 b in the firstdirection X are continuous with the flange 11 s of the drain framefinger 11P that is located closest to the first lateral side surface 33and the flange 11 s of the drain frame finger 11Q. The thickness of thedrain coupling portion 11 b at the two ends 11 t is less than thethickness of other parts excluding the end 11 k and the two ends 11 t ofthe drain coupling portion 11 b and equal to the thickness TD5 of theflanges 11 s. The two ends 11 t of the drain coupling portion 11 b arenot exposed from the back surface 32 of the encapsulation resin 30.

Furthermore, the flange 11 s of the drain frame finger 11P that iscloses to the first lateral side surface 33 and the flange 11 s of thedrain frame finger 11Q are continuous with the second tie bar portions11 i and 11 j. The length in the second direction Y of the two ends 11 tof the drain coupling portion 11 b and the length in the seconddirection Y of the flanges 11 s can be set in any manner. For example,the length in the second direction Y of the two ends 11 t of the draincoupling portion 11 b and the flanges 11 s may be set to form a gapextending in the second direction Y from the two ends 11 t of the draincoupling portion 11 b to the flanges 11 s. The length of the flanges 11s in the second direction Y may be set to form a gap extending from theflanges 11 s to the second tie bar portion 11 i, 11 j in the seconddirection Y.

As shown in FIG. 23, the drain coupling portion 11 b is exposed from theback surface 32 of the encapsulation resin 30. Thus, the area exposedfrom the back surface 32 of the drain coupling portion 11 b becomesgreater than the area (see FIG. 9) exposed from the back surface 32 ofthe drain coupling portion 11 b of the first embodiment.

The semiconductor device 1 of the present embodiment has the followingadvantages.

(30) As the width WCD of the drain coupling portion 11 b increases, thearea of the drain coupling portion 11 b exposed from the back surface 32of the encapsulation resin 30 increases. Thus, the heat of the drainframe 11 and the heat of the transistor 20 are easily dissipated to theoutside of the semiconductor device 1 through the drain frame 11. Thisensures that the temperature of the semiconductor device 1 does notbecome excessively high.

(31) The lengths LFD and LFDE of the drain frame fingers 11P and 11Q aredecreased. This limits deformation of the drain frame fingers 11P and11Q in the height direction Z when the transistor 20 is mounted on thedrain frame fingers 11P and 11Q.

(32) The two ends 11 t of the drain coupling portion 11 b have athickness that is less than the thickness of parts other than the endilk and the two ends 11 t of the drain coupling portion 11 b. Further,the two ends 11 t are not exposed from the back surface 32 of theencapsulation resin 30. According to such a configuration, the surfacesof the two ends 11 t of the drain coupling portion 11 b located towardthe back surface 32 face and contact the encapsulation resin 30. Thus,the two ends 11 t limit movement of the drain coupling portion 11 btoward the back surface 32. This further limits projection of the draincoupling portion 11 b out of the back surface 32.

(33) The two ends 11 t of the drain coupling portion 11 b, the flanges11 s of the drain frame finger 11 c, and the second tie bar portions 11i, 11 j are continuously formed. According to such a configuration, therigidity of the drain frame finger 11 c can be improved. This reducescurving of the drain frame fingers 11 c.

Other Embodiments

The description related to each embodiment described above is anillustration of a mode that can be taken by the semiconductor device ofthe present invention, and is not intended to limit the mode thereof.The semiconductor device of the present invention may adopt a mode inwhich, for example, a modified example of each embodiment describedabove and at least two modified examples that do not contradict eachother are combined, as described below.

Combination of Embodiments

The heat dissipation plate 130 of the third embodiment may be applied tothe semiconductor device 1 of the second embodiment and the fourthembodiment.

The drain frame 11 of the fourth embodiment may be applied to thesemiconductor device 1 of the second embodiment.

Lead Frame

In each embodiment described above, the configuration of the lead frame10 may be changed as described below.

As shown in FIG. 24, the thickness of the source coupling portion 12 bof the source frame 12 is equal to the thickness of the source terminal12 a. In other words, the thickness of the source coupling portion 12 bis not decreased (shaded region not added). As a result, the sourcecoupling portion 12 b is exposed from the back surface 32 of theencapsulation resin 30, as shown in FIG. 25. Thus, the heat of thesource frame 12 and the heat of the transistor 20 are easily dissipatedto the outside of the semiconductor device 1 through the source frame 12as the area of the source frame 12 exposed from the back surface 32 ofthe encapsulation resin 30 increases. This ensures that the temperatureof the semiconductor device 1 does not become excessively high.

As shown in FIG. 26, the width WCS of the source coupling portion 12 bof the source frame 12 is greater than the width WCS (see e.g., FIG. 3)of the source coupling portion 12 b of each embodiment. As a result, thelengths LFD and LFDE of the drain frame fingers 11P and 11Q are lessthan the lengths LFD and LFDE of the drain frame fingers 11P and 11Q inthe above embodiments, and the length LFG of the gate frame finger 13 cis greater than the length LFG of the gate frame finger 13 c in theabove embodiments. The transistor 20 is arranged closer to the firstlongitudinal side surface 35 of the encapsulation resin 30 than thetransistor 20 in the above embodiments.

The thickness TS1 of the source coupling portion 12 b is equal to thethickness TS2 of the source terminals 12 a. In other words, thethickness of the source coupling portion 12 b is not reduced (shadedregion is not added). As a result, the source coupling portion 12 b isexposed from the back surface 32 of the encapsulation resin 30, as shownin FIG. 27. Thus, the heat of the source frame 12 and the heat of thetransistor 20 are more easily dissipated to the outside of thesemiconductor device 1 through the source frame 12 as the area exposedfrom the back surface 32 increases in the source frame 12. This furtherensures that the temperature of the semiconductor device 1 does notbecome excessively high. The thickness TS1 of the source couplingportion 12 b may be less than the thickness TS2 of the source terminal12 a. Thus, the source coupling portion 12 b is not exposed from theback surface 32 of the encapsulation resin 30.

As shown in FIG. 28, the width WCD of the drain coupling portion 11 b ofthe drain frame 11 is greater than the width WCD (see e.g., FIG. 3) ofthe drain coupling portion 11 b of each embodiment, and the width WCS ofthe source coupling portion 12 b of the source frame 12 is greater thanthe width WCS (see e.g., FIG. 3) of the source coupling portion 12 b ofeach embodiment. As a result, the lengths LFD and LFDE of the drainframe fingers 11P and 11Q are less than the lengths LFD and LFDE (seee.g., FIG. 3) of the drain frame fingers 11P and 11Q in the aboveembodiments, and the length LFG of the gate frame finger 13 c is greaterthan the length LFG of the gate frame finger 13 c in the aboveembodiments. The transistor 20 is arranged closer to the firstlongitudinal side surface 35 of the encapsulation resin 30 than thetransistor 20 of the above embodiments.

The thickness TS1 of the source coupling portion 12 b is equal to thethickness TS2 of the source terminal 12 a. In other words, the thicknessof the source coupling portion 12 b is not reduced (shaded region is notadded). As a result, the source coupling portion 12 b is exposed fromthe back surface 32 of the encapsulation resin 30, as shown in FIG. 29.Furthermore, the area in which the drain frame 11 is exposed from theback surface 32 increases as the width WCDR of the drain couplingportion 11 b increases. According to such a configuration, the heat ofthe drain frame 11 and the source frame 12 as well as the heat of thetransistor 20 are easily dissipated to the outside of the semiconductordevice 1 through the drain frame 11 and the source frame 12. Thisfurther ensures that the temperature of the semiconductor device 1 doesnot become excessively high. The thickness TS1 of the source couplingportion 12 b may be less than the thickness TS2 of the source terminal12 a. Thus, the source coupling portion 12 b is not exposed from theback surface 32 of the encapsulation resin 30.

As shown in FIG. 30, the thickness TS1 of each source frame finger 12 cat the end closer to the source coupling portion 12 b may be equal tothe thickness TS2 of the source terminals 12 a. In other words, thethickness of the portion of each source frame finger 12 c that overlapsthe distal portion 11 h of each drain frame fingers 11 c in the firstdirection X may be reduced.

The thickness TD5 of the flanges 11 s of the first section 11 m in thedrain frame finger 11 c can be changed. For example, the thickness TD5of the flanges 11 s may be equal to the thickness TD4 of the base 11 r.In this case, the flanges 11 s are exposed from the back surface 32 ofthe encapsulation resin 30 together with the base 11 r.

At least one drain frame finger 11 c may have a configuration in whichthe flanges 11 s are omitted from the first section 11 m. In this case,as shown in FIG. 31, the drain frame finger 11 c has a uniform thicknessWFD2.

As shown in FIG. 31, the end 11 k may be omitted from the drain couplingportion 11 b.

At least one of the tie bar portions 11 d, 11 i, 11 j, 12 d, and 13 dmay be exposed from the back surface 32 of the encapsulation resin 30.The width of each of the tie bar portions 11 d, 11 i, 11 j, 12 d, and 13d can be set in any manner. For example, the width of each of the tiebar portions 11 d, 11 i, 11 j, 12 d, and 13 d may be greater than thewidth WFD1 or the width WFD2 of the drain frame finger 11 c.

The second tie bar portions 11 i and 11 j may be omitted from the drainframe 11.

The entire drain frame finger 11 c does not have to be exposed from theback surface 32 of the encapsulation resin 30. In this case, thethickness of the drain frame finger 11 c is equal to the thickness TD1.

The entire drain frame finger 11 c is not exposed from the back surface32 of the encapsulation resin 30, and the source frame fingers 12 c maybe exposed from the back surface 32 of the encapsulation resin 30. Inthis case, the thickness TS1 of the source frame finger 12 c is equal tothe thickness TS2.

Transistor

In each embodiment described above, the side wall 54 may be omitted fromthe transistor 20. In this case, the distance DPgf between the gateelectrode 80 and the source field plate 45 can be controlled based onthe thickness of the gate insulating film 52.

In each embodiment described above, at least one of the floating plate46 between the source and the gate or the source field plate 45 betweenthe gate and the drain may be omitted from the transistor 20.

In each embodiment described above, the drain electrode pads 21P and thesource electrode pads 22 on the front surface 20 a of the transistor 20may be divided into segments in the second direction Y. For example, asshown in FIG. 32, the drain electrode pads 21P and the source electrodepads 22 are each divided into two in the second direction Y. Thus, thedrain electrode pads 21, the source electrode pads 22, and the gateelectrodes 23 all have the same shape.

In each embodiment described above, the drain electrode finger 71 of thedrain electrode 70 may be longer than the source electrode finger 62 ofthe source electrode 60. In this case, as shown in FIG. 33, one drainelectrode finger 71 of the drain electrode 70 may project outward fromone end 82 a of the gate electrode finger 82 of the gate electrode 80 inthe third direction V. Furthermore, the other drain electrode finger 71of the drain electrode 70 may project outward from the other end 82 b ofthe gate electrode finger 82 of the gate electrode 80 in the thirddirection V. In FIG. 33, a first projecting distance LDE1 with respectto the one end 82 a of the gate electrode finger 82 in the drainelectrode finger 71 is the same as a second projecting distance LDE2with respect to the other end 82 b of the gate electrode finger 82 inthe drain electrode finger 71. The first projecting distance LDE1 andthe second projecting distance LDE2 are, for example, greater than orequal to 3 μm and less than or equal to 45 μm. The first projectingdistance LDE1 and the second projecting distance LDE2 may be set in anymanner.

In the transistor 20 of each embodiment described above, the firstprojecting distance LDE1 and the second projecting distance LDE2 may begreater than or equal to a shortest distance LGD between the gateelectrode finger 82 of the gate electrode 80 and the drain electrodefinger 71 of the drain electrode 70. In the transistor 20 of FIG. 33,the first projecting distance LDE1 and the second projecting distanceLDE2 are greater than the shortest distance LGD. For example, a ratio(LDE1/LGD, LDE2/LGD) of the first projecting distance LDE1 (secondprojecting distance LDE2) and the shortest distance LGD may be greaterthan or equal to one and less than or equal to five. The shortestdistance LGD is, for example, greater than or equal to 3 μm and lessthan or equal to 15 μm.

According to such a configuration, the electric field intensity isdecreased when the drain side of the transistor 20 is inactive. Thisincreases the dielectric breakdown strength of the transistor 20.

In the transistor 20 of each embodiment described above, the source wire91 may be extended on the source electrode finger 62 along the thirddirection V and connected to the adjacent source wire 91 on the outerside of the source electrode finger 62, as shown in FIG. 33. In the samemanner as the source wire 91, the drain wire 92 may also be extended onthe drain electrode finger 71 along the third direction V and connectedto the adjacent drain wire 92 on the outer side of the drain electrodefinger 71.

Application of Semiconductor Device

The semiconductor device 1 may be applied to a motor drive circuit suchas a motor drive circuit of a single phase full wave motor, a motordrive circuit of a three-phase-drive brushless motor, and a motor drivecircuit of a stepping motor.

EMBODIMENTS

Technical ideas that can be recognized from the embodiments and modifiedexamples will now be described.

Embodiment A1

The semiconductor device according to claim 1, wherein:

the drain frame, the source frame, and the gate frame are formed throughan etching process, and

parts of the drain frame, the source frame, and the gate frame that arenot exposed from a back surface of the encapsulation resin is formedthrough a half-etching process.

Embodiment A2

The semiconductor device according to claim 1, wherein the ones of thedrain frame fingers located at two ends in the first direction eachinclude a tie bar portion extending in the second direction.

Embodiment B1

The semiconductor device according to claim 37 or 38, where a distanceDPGf between the gate electrode and the conductive layer is less than orequal to 1 μm.

Embodiment B2

The semiconductor device according to claim 37 or 38, wherein a lengthLfp of the conductive layer and a distance DPgd between the gateelectrode and the drain electrode are in a relationship that satisfiesLfp<1/3 DPgd.

Embodiment B3

The semiconductor device according to any one of claims 1 to 30, whereinthe transistor includes:

a nitride semiconductor layer obtained by stacking a buffer layer, anelectron travel layer, and an electron supply layer on a substrate;

a gate electrode finger that includes at least one end and extends alonga front surface of the nitride semiconductor layer; and

a drain electrode finger that includes one end located at a side that isthe same as the at least one end of the gate electrode finger andextends along the gate electrode finger, wherein the one end of thedrain electrode finger projects outward from the one end of the gateelectrode finger.

Embodiment B4 The semiconductor device according to embodiment B3,wherein

the gate electrode finger and the drain electrode finger each includeanother end opposite to the one end,

the drain electrode finger is longer than the gate electrode finger, and

the other end of the drain electrode finger is projected outward fromthe other end of the gate electrode finger.

Embodiment B5

The semiconductor device according to embodiment B3 or B4, wherein aprojecting distance of the one end of the drain electrode finger isgreater than or equal to a shortest distance between the gate electrodefinger and the drain electrode finger.

DESCRIPTION OF REFERENCE CHARACTERS

-   -   1) semiconductor device, 10) lead frame, 11) drain frame, 11 a)        drain terminal, 11 b) drain coupling portion, 11 c) drain frame        finger, 11P) drain frame finger, 11Q) drain frame finger, 11 d)        first tie bar portion, 11 e) front surface, 11 h) distal        portion, 11 i and 11 j) second tie bar portions, 11 k) end, 11        m) first section, 11 n) second section, 11 r) base, 11 s)        flange, 12) source frame, 12 a) source terminal, 12 b) source        coupling portion, 12 c) source frame finger, 12 d) tie bar        portion, 12 e) front surface, 13) gate frame, 13 a) gate        terminal, 13 b) gate coupling portion, 13 c) gate frame finger,        13 d) tie bar portion, 13 e) front surface, 20) transistor, 20        a) front surface (other surface), 20 b) back surface (one        surface), 21) drain electrode pad, 21P) drain electrode pad,        21Q) drain electrode pad, 22) source electrode pad, 23) gate        electrode pad, 30) encapsulation resin, 31) front surface, 32)        back surface, 40) substrate, 41) buffer layer, 41 a) first        buffer layer, 41 b) second buffer layer, 42) electron travel        layer, 43) electron supply layer, 50) insulating layer, 52) gate        insulating film, 54) side wall, 60) source electrode, 62) source        electrode finger, 70) drain electrode, 71) drain electrode        finger, 80) gate electrode, 82) gate electrode finger, 91)        source wire, 92) drain wire, 93) gate wire, 130) heat        dissipation plate

The invention claimed is:
 1. A semiconductor device comprising: aplurality of first lead frame fingers connected to first electrodes onone surface of a transistor, and a plurality of second lead framefingers connected to second electrodes on the one surface of thetransistor, wherein the first lead frame fingers are spaced apart fromeach other in a first direction, and extended in a second direction thatis orthogonal to the first direction in a plan view, the second leadframe fingers are spaced apart from each other in the first direction,and extended in the second direction, the first lead frame fingers andthe second lead frame fingers are alternately arranged in the firstdirection, each of the first lead frame fingers includes a first sectionthat does not overlap with the second lead frame fingers and a secondsection that overlaps with the second lead frame fingers as viewed inthe first direction, a width of the first section on average is greaterthan a width of the second section on average, the first sectionincludes a base that is continuous with the second section and a flangethat projects from the base in the first direction, and a thickness ofthe flange is less than a thickness of the base.
 2. The semiconductordevice according to claim 1, wherein a length of the second lead framefingers is less than a length of the first lead frame fingers in thesecond direction.
 3. The semiconductor device according to claim 1,wherein each of the first section and the second section has a generallyrectangular shape in a plan view.
 4. The semiconductor device accordingto claim 1, wherein the first lead frame fingers are drain framefingers, the first electrodes are drain electrode pads, the second leadframe fingers are source frame fingers, and the second electrodes aresource electrode pads.
 5. The semiconductor device according to claim 1,further comprising an encapsulation resin that is rectangular andencapsulates the transistor, the first lead frame fingers, and thesecond lead frame fingers so that part of the first lead frame fingersis exposed from a back surface.
 6. The semiconductor device according toclaim 5, further comprising: a plurality of first lead frame terminalsformed on one side of the encapsulation resin in the second directionand spaced apart from each other in the first direction, and a pluralityof second lead frame terminals formed on another side of theencapsulation resin in the second direction and spaced apart from eachother in the first direction.
 7. The semiconductor device according toclaim 6, wherein the first lead frame terminals are drain terminals, andthe second lead frame terminals are source terminals.
 8. Thesemiconductor device according to claim 6, wherein the first section islocated toward the first lead frame terminals, and a second sectioncontinuously extends from the first section toward the second lead frameterminals, and the first section is located closer to the first leadframe terminals than a distal end of each second lead frame finger. 9.The semiconductor device according to claim 1, wherein flangesprojecting from opposite sides of the base in the first direction arepresent, and the flange with a thickness less than a thickness of thebase is one of the flanges that project from opposite sides of the basein the first direction.
 10. The semiconductor device according to claim1, wherein a portion of each second lead frame finger overlapped withthe first lead frame fingers as viewed in the first direction has athickness that is less than a maximum thickness of the first lead framefingers.
 11. The semiconductor device according to claim 1, furthercomprising: a first lead frame coupling portion that couples the firstlead frame fingers, wherein the first lead frame fingers extend in thesecond direction from the first lead frame coupling portion.
 12. Thesemiconductor device according to claim 1, further comprising: a secondlead frame coupling portion that couples the second lead frame fingers,wherein the second lead frame fingers extend in the second directionfrom the second lead frame coupling portion.
 13. The semiconductordevice according to claim 1, further comprising: a third lead framefinger connected to a third electrode on the one surface of thetransistor.
 14. The semiconductor device according to claim 13, whereinthe third lead frame finger is a gate frame finger, and the thirdelectrode is a gate electrode pad.
 15. The semiconductor deviceaccording to claim 13, wherein a length of the third lead frame fingeris shorter than a length of each second lead frame finger in the seconddirection.
 16. The semiconductor device according to claim 6, whereineach of the second electrodes includes a first end and a second end,with the first end being located closer to the first lead frameterminals than is the second end, and the second end being locatedcloser to the second lead frame terminals than is the first end, and adistal portion of each of the second lead frame fingers is located atthe first end of each of the second electrodes.
 17. The semiconductordevice according to claim 1, wherein the width of the first section isconstant along the second direction, and the width of the second sectionis constant along the second direction.